FEAT: menu Help (About modal + hướng dẫn sử dụng) + Tools Preferences (theme/language/button font size)

app/static/js/app.jsx

@@ -6469,6 +6469,155 @@ const SystemManagerModal = ({
   }, "Xóa")))))))));
 };
 
+/* ═══════════════════════════════════════════════════════════════════
+   ABOUT / HELP / PREFERENCES MODALS (menu Help + Tools → Preferences)
+   ═══════════════════════════════════════════════════════════════════ */
+const APP_VERSION = '1.0.0'; // khớp src-tauri/tauri.conf.json
+
+const AboutModal = ({ isOpen, onClose }) => {
+  if (!isOpen) return null;
+  return (
+    <div className="fixed inset-0 z-[9999] flex items-center justify-center bg-black/70 backdrop-blur-sm" onClick={onClose}>
+      <div className="bg-[#1e1e24] border border-zinc-700 rounded-xl shadow-2xl w-full max-w-md p-6 text-slate-200" onClick={e => e.stopPropagation()}>
+        <div className="flex items-center gap-3 mb-4">
+          <div className="w-12 h-12 rounded-lg bg-gradient-to-br from-cyan-500 to-violet-600 flex items-center justify-center text-white text-xl font-black shadow-lg">SF</div>
+          <div>
+            <h2 className="text-lg font-bold text-white">SonicForge Studio</h2>
+            <p className="text-xs text-zinc-400">Professional DAW — v{APP_VERSION}</p>
+          </div>
+        </div>
+        <div className="space-y-2 text-sm">
+          <p className="text-zinc-300 leading-relaxed">Phần mềm sản xuất âm nhạc (DAW) — soạn nhạc, ghi âm, chỉnh sửa MIDI/Audio, SoundFont &amp; VST, trộn và master.</p>
+          <div className="pt-2 border-t border-zinc-800 space-y-1 text-xs">
+            <div className="flex items-center gap-2"><span className="text-zinc-500 w-20 shrink-0">Developer</span><span className="text-cyan-400 font-semibold">Lộc Phạm</span></div>
+            <div className="flex items-center gap-2"><span className="text-zinc-500 w-20 shrink-0">Email</span><a href="mailto:tranloclqd@gmail.com" className="text-cyan-400 hover:underline">tranloclqd@gmail.com</a></div>
+            <div className="flex items-center gap-2"><span className="text-zinc-500 w-20 shrink-0">Version</span><span className="text-zinc-300">{APP_VERSION}</span></div>
+            <div className="flex items-center gap-2"><span className="text-zinc-500 w-20 shrink-0">Build</span><span className="text-zinc-300">Standalone (Tauri v2 + PyInstaller)</span></div>
+          </div>
+        </div>
+        <div className="mt-5 flex justify-end">
+          <button onClick={onClose} className="px-4 py-1.5 bg-cyan-700 hover:bg-cyan-600 rounded text-xs font-bold text-white transition">Đóng</button>
+        </div>
+      </div>
+    </div>
+  );
+};
+
+const HelpModal = ({ isOpen, onClose, lang }) => {
+  if (!isOpen) return null;
+  const vi = lang !== 'en';
+  const sections = vi ? [
+    { title: '🚀 Bắt đầu nhanh', body: 'Nhấn phím Cách (Space) để Play/Pause. Nhấn phím / để dừng. Dùng nút Record (●) để ghi âm/MIDI. Tạo track mới từ menu Track hoặc nút "+ Add Track".' },
+    { title: '🎹 MIDI & ARM', body: 'Bật nút ARM đỏ trên track để nhận phím từ MIDI keyboard. Vào menu Tools → MIDI Devices để chọn thiết bị. Khi ARM + bấm phím, âm preview phát và VU meter nhảy theo trường độ.' },
+    { title: '🎼 Piano Roll', body: 'Nhấp đúp vào MIDI item để mở Piano Roll. Dùng Ctrl+scroll hoặc nút +/− để zoom. Nhấp để vẽ note, kéo để di chuyển, Ctrl+kéo để copy. Phím tắt: C (vẽ), E (tẩy), Space (nghe).' },
+    { title: '🎛️ FX & Master', body: 'Chọn track → nút FX để mở FX Rack (thêm EQ, compressor...). Bấm nút PWR ở Master để mở Mastering Panel: EQ 4 băng, compressor, limiter. Mọi thay đổi áp dụng realtime.' },
+    { title: '🧪 SoundFont & VST', body: 'Vào Tools → Plugin Manager để quét SoundFont (.sf2/.sf3) và VSTi. Track MIDI dùng SoundFont làm nhạc cụ — chọn instrument từ nút Synth trên track.' },
+    { title: '🤖 AI', body: 'Tools → Config AI Providers để cấu hình API (OpenAI, Gemini, Ollama...). Dùng AI Prompt Generator (nút ✨) để sinh MIDI/ý tưởng; AI MIDI Preset Manager để lưu preset.' },
+    { title: '💾 Lưu & Xuất', body: 'Ctrl+S lưu project (cloud/temp), Ctrl+Shift+S Save As. Export WAV qua nút Export — chọn vùng, format, bitrate rồi Render.' },
+    { title: '⌨️ Phím tắt', body: 'Space: Play/Pause · /: Stop · Ctrl+Z/Y: Undo/Redo · Ctrl+C/X/V: Copy/Cut/Paste · Ctrl+S: Save · Ctrl+N: New · S: Split · Ctrl+E: Edit in new tab · Ctrl+wheel: zoom timeline' },
+  ] : [
+    { title: '🚀 Quick start', body: 'Press Space to Play/Pause. Press / to stop. Use Record (●) to capture audio/MIDI. Add tracks from the Track menu or the "+ Add Track" button.' },
+    { title: '🎹 MIDI & ARM', body: 'Enable the red ARM button on a track to receive keys from a MIDI keyboard. Go to Tools → MIDI Devices to pick your device. When ARM + key press, preview audio plays and the VU meter animates for the note length.' },
+    { title: '🎼 Piano Roll', body: 'Double-click a MIDI item to open the Piano Roll. Use Ctrl+scroll or +/− buttons to zoom. Click to draw notes, drag to move, Ctrl+drag to copy. Shortcuts: C (draw), E (erase), Space (listen).' },
+    { title: '🎛️ FX & Master', body: 'Select a track → FX button to open the FX Rack (EQ, compressor...). Press the PWR button on the Master to open the Mastering Panel: 4-band EQ, compressor, limiter — all realtime.' },
+    { title: '🧪 SoundFont & VST', body: 'Tools → Plugin Manager scans SoundFonts (.sf2/.sf3) and VSTi. MIDI tracks use SoundFonts as instruments — pick one from the Synth button on the track.' },
+    { title: '🤖 AI', body: 'Tools → Config AI Providers to set up APIs (OpenAI, Gemini, Ollama...). Use the AI Prompt Generator (✨) to create MIDI/ideas; AI MIDI Preset Manager stores presets.' },
+    { title: '💾 Save & Export', body: 'Ctrl+S saves the project (cloud/temp), Ctrl+Shift+S Save As. Export WAV via the Export button — pick range, format, bitrate, then Render.' },
+    { title: '⌨️ Shortcuts', body: 'Space: Play/Pause · /: Stop · Ctrl+Z/Y: Undo/Redo · Ctrl+C/X/V: Copy/Cut/Paste · Ctrl+S: Save · Ctrl+N: New · S: Split · Ctrl+E: Edit in new tab · Ctrl+wheel: zoom timeline' },
+  ];
+  return (
+    <div className="fixed inset-0 z-[9999] flex items-center justify-center bg-black/70 backdrop-blur-sm" onClick={onClose}>
+      <div className="bg-[#1e1e24] border border-zinc-700 rounded-xl shadow-2xl w-full max-w-2xl max-h-[85vh] flex flex-col text-slate-200" onClick={e => e.stopPropagation()}>
+        <div className="flex items-center justify-between px-5 py-3 border-b border-zinc-800 shrink-0">
+          <h2 className="text-base font-bold text-white">{vi ? 'Hướng dẫn sử dụng SonicForge Studio' : 'SonicForge Studio User Guide'}</h2>
+          <button onClick={onClose} className="w-6 h-6 rounded hover:bg-zinc-700 text-zinc-400 hover:text-white text-sm">✕</button>
+        </div>
+        <div className="overflow-y-auto px-5 py-4 space-y-3">
+          {sections.map((s, i) => (
+            <div key={i} className="bg-zinc-900/60 border border-zinc-800 rounded-lg p-3">
+              <h3 className="text-sm font-bold text-cyan-400 mb-1">{s.title}</h3>
+              <p className="text-xs text-zinc-300 leading-relaxed">{s.body}</p>
+            </div>
+          ))}
+        </div>
+        <div className="px-5 py-3 border-t border-zinc-800 flex justify-end shrink-0">
+          <button onClick={onClose} className="px-4 py-1.5 bg-cyan-700 hover:bg-cyan-600 rounded text-xs font-bold text-white transition">{vi ? 'Đóng' : 'Close'}</button>
+        </div>
+      </div>
+    </div>
+  );
+};
+
+const PreferencesModal = ({ isOpen, onClose, prefs, onPrefsChange }) => {
+  if (!isOpen) return null;
+  const vi = prefs.language !== 'en';
+  const themes = [
+    { id: 'dark', name: vi ? 'Tối (mặc định)' : 'Dark (default)', swatch: 'from-zinc-700 to-zinc-900', ring: 'ring-cyan-400' },
+    { id: 'midnight', name: vi ? 'Đêm xanh' : 'Midnight', swatch: 'from-sky-800 to-slate-950', ring: 'ring-sky-400' },
+    { id: 'forest', name: vi ? 'Rừng xanh' : 'Forest', swatch: 'from-emerald-700 to-green-950', ring: 'ring-emerald-400' },
+    { id: 'violet', name: vi ? 'Tím' : 'Violet', swatch: 'from-violet-700 to-purple-950', ring: 'ring-violet-400' },
+    { id: 'graphite', name: vi ? 'Than chì' : 'Graphite', swatch: 'from-zinc-600 to-neutral-900', ring: 'ring-zinc-300' },
+  ];
+  const set = (k, v) => onPrefsChange({ ...prefs, [k]: v });
+  return (
+    <div className="fixed inset-0 z-[9999] flex items-center justify-center bg-black/70 backdrop-blur-sm" onClick={onClose}>
+      <div className="bg-[#1e1e24] border border-zinc-700 rounded-xl shadow-2xl w-full max-w-md max-h-[85vh] overflow-y-auto p-5 text-slate-200" onClick={e => e.stopPropagation()}>
+        <div className="flex items-center justify-between mb-4">
+          <h2 className="text-base font-bold text-white">{vi ? 'Tùy chọn (Preferences)' : 'Preferences'}</h2>
+          <button onClick={onClose} className="w-6 h-6 rounded hover:bg-zinc-700 text-zinc-400 hover:text-white text-sm">✕</button>
+        </div>
+
+        {/* Theme */}
+        <div className="mb-5">
+          <h3 className="text-xs font-bold text-zinc-400 uppercase tracking-wider mb-2">{vi ? '🎨 Chủ đề màu' : '🎨 Theme'}</h3>
+          <div className="grid grid-cols-1 gap-1.5">
+            {themes.map(th => (
+              <button key={th.id} onClick={() => set('theme', th.id)}
+                className={`flex items-center gap-2.5 px-2.5 py-2 rounded-lg border text-xs text-left transition ${prefs.theme === th.id ? 'border-cyan-500 bg-zinc-800' : 'border-zinc-700 bg-zinc-900 hover:bg-zinc-800'}`}>
+                <span className={`w-6 h-6 rounded-md bg-gradient-to-br ${th.swatch} ring-1 ring-black/40 shrink-0 ${prefs.theme === th.id ? `ring-2 ${th.ring}` : ''}`}></span>
+                <span className="text-zinc-200">{th.name}</span>
+                {prefs.theme === th.id && <span className="ml-auto text-cyan-400 text-[10px] font-bold">✓</span>}
+              </button>
+            ))}
+          </div>
+        </div>
+
+        {/* Language */}
+        <div className="mb-5">
+          <h3 className="text-xs font-bold text-zinc-400 uppercase tracking-wider mb-2">{vi ? '🌐 Ngôn ngữ' : '🌐 Language'}</h3>
+          <div className="flex gap-1.5">
+            {[{ id: 'vi', label: 'Tiếng Việt' }, { id: 'en', label: 'English' }].map(l => (
+              <button key={l.id} onClick={() => set('language', l.id)}
+                className={`flex-1 px-2 py-1.5 rounded-lg border text-xs font-semibold transition ${prefs.language === l.id ? 'border-cyan-500 bg-cyan-900/40 text-cyan-300' : 'border-zinc-700 bg-zinc-900 text-zinc-400 hover:bg-zinc-800'}`}>
+                {l.label}
+              </button>
+            ))}
+          </div>
+          <p className="text-[10px] text-zinc-500 mt-1">{vi ? 'Áp dụng ngay cho menu & hướng dẫn.' : 'Applies immediately to menus & guide.'}</p>
+        </div>
+
+        {/* Button font size */}
+        <div className="mb-5">
+          <h3 className="text-xs font-bold text-zinc-400 uppercase tracking-wider mb-2">{vi ? '🔠 Cỡ chữ nút bấm' : '🔠 Button font size'}</h3>
+          <div className="flex gap-1.5">
+            {[{ id: 'sm', label: vi ? 'Nhỏ' : 'Small' }, { id: 'md', label: vi ? 'Vừa' : 'Medium' }, { id: 'lg', label: vi ? 'Lớn' : 'Large' }].map(f => (
+              <button key={f.id} onClick={() => set('buttonFontSize', f.id)}
+                className={`flex-1 px-2 py-1.5 rounded-lg border text-xs font-semibold transition ${prefs.buttonFontSize === f.id ? 'border-cyan-500 bg-cyan-900/40 text-cyan-300' : 'border-zinc-700 bg-zinc-900 text-zinc-400 hover:bg-zinc-800'}`}>
+                {f.label}
+              </button>
+            ))}
+          </div>
+        </div>
+
+        <div className="flex justify-end gap-2 pt-2 border-t border-zinc-800">
+          <button onClick={onClose} className="px-3 py-1.5 bg-zinc-700 hover:bg-zinc-600 rounded text-xs font-bold text-white transition">{vi ? 'Hủy' : 'Cancel'}</button>
+          <button onClick={onClose} className="px-4 py-1.5 bg-cyan-700 hover:bg-cyan-600 rounded text-xs font-bold text-white transition">{vi ? 'Lưu & Đóng' : 'Save & Close'}</button>
+        </div>
+      </div>
+    </div>
+  );
+};
+
 const AIPresetModal = ({ isOpen, onClose }) => {
   if (!isOpen) return null;
 
@@ -15562,6 +15711,51 @@ const App = () => {
   const [aiPresetModalOpen, setAiPresetModalOpen] = useState(false);
   const [aiPresetVersion, setAiPresetVersion] = useState(0);
   const [showMasteringModal, setShowMasteringModal] = useState(false);
+  // ── Help / About / Preferences (menu Help + Tools) ──
+  const [aboutModalOpen, setAboutModalOpen] = useState(false);
+  const [helpModalOpen, setHelpModalOpen] = useState(false);
+  const [preferencesModalOpen, setPreferencesModalOpen] = useState(false);
+  const [prefs, setPrefs] = useState(() => {
+    try {
+      const saved = localStorage.getItem('sf_prefs');
+      if (saved) return JSON.parse(saved);
+    } catch (e) { }
+    return { theme: 'dark', language: 'vi', buttonFontSize: 'md' };
+  });
+  // Áp dụng theme + font size lên <html> ngay khi đổi
+  useEffect(() => {
+    try {
+      document.documentElement.setAttribute('data-theme', prefs.theme || 'dark');
+      document.documentElement.setAttribute('data-btnfont', prefs.buttonFontSize || 'md');
+      localStorage.setItem('sf_prefs', JSON.stringify(prefs));
+    } catch (e) { }
+  }, [prefs]);
+  // Load preferences từ server (nếu có tài khoản) khi khởi động
+  useEffect(() => {
+    let cancelled = false;
+    if (window.SonicAPI && window.SonicAPI.getPreferences) {
+      window.SonicAPI.getPreferences().then(res => {
+        if (cancelled || !res || !res.success || !res.preferences) return;
+        const p = res.preferences;
+        if (p.theme || p.language || p.buttonFontSize) {
+          setPrefs(prev => ({
+            theme: p.theme || prev.theme,
+            language: p.language || prev.language,
+            buttonFontSize: p.buttonFontSize || prev.buttonFontSize
+          }));
+        }
+      }).catch(() => { });
+    }
+    return () => { cancelled = true; };
+  }, []);
+  // Lưu preferences lên server khi đổi
+  const handlePrefsChange = (next) => {
+    setPrefs(next);
+    try { localStorage.setItem('sf_prefs', JSON.stringify(next)); } catch (e) { }
+    if (window.SonicAPI && window.SonicAPI.savePreferences) {
+      window.SonicAPI.savePreferences(next).catch(() => { });
+    }
+  };
   // Unified FX Rack target context (unified_fx_rack_panel.md): { trackId, trackName } | null
   const [fxRackTarget, setFxRackTarget] = useState(null);
   window.__openFxRack = (trackId, trackName) => setFxRackTarget({ trackId, trackName });
@@ -26282,13 +26476,25 @@ STRICT CONSTRAINTS:
         setPluginManagerModalOpen(true);
         window.SonicAPI.listPlugins().then(data => setPluginsData(data)).catch(() => {});
       }
+    }, {
+      sep: true
+    }, {
+      label: 'Preferences...',
+      icon: 'settings-2',
+      action: () => setPreferencesModalOpen(true)
     }]
   }, {
     label: 'Help',
     items: [{
-      label: 'About SonicForge',
+      label: 'Hướng dẫn sử dụng...',
+      icon: 'book-open',
+      action: () => setHelpModalOpen(true)
+    }, {
+      sep: true
+    }, {
+      label: 'About SonicForge Studio...',
       icon: 'info',
-      action: () => showToast('SonicForge Studio v1.0 - Professional DAW', 'info')
+      action: () => setAboutModalOpen(true)
     }]
   }].map(menu => /*#__PURE__*/React.createElement("div", {
     key: menu.label,
@@ -29264,6 +29470,18 @@ STRICT CONSTRAINTS:
       const active = providers.find(p => p.is_active) || providers[0];
       if (active) setSelectedProviderId(active.id);
     }
+  }), /*#__PURE__*/React.createElement(AboutModal, {
+    isOpen: aboutModalOpen,
+    onClose: () => setAboutModalOpen(false)
+  }), /*#__PURE__*/React.createElement(HelpModal, {
+    isOpen: helpModalOpen,
+    onClose: () => setHelpModalOpen(false),
+    lang: prefs.language
+  }), /*#__PURE__*/React.createElement(PreferencesModal, {
+    isOpen: preferencesModalOpen,
+    onClose: () => setPreferencesModalOpen(false),
+    prefs: prefs,
+    onPrefsChange: handlePrefsChange
   }), /*#__PURE__*/React.createElement(SystemManagerModal, {
     isOpen: systemManagerModalOpen,
     onClose: () => setSystemManagerModalOpen(false)

app/templates/index.html

@@ -43,7 +43,7 @@
     <script src="/static/js/services/midiExtractor.js?v=202607281052"></script>
     <script src="/static/js/services/promptTemplateManager.js?v=202607281039"></script>
     <script src="/static/js/services/undoRedoEngine.js?v=202607290941"></script>
-    <script src="/static/js/app.precompiled.js?v=202608081400" defer></script>
+    <script src="/static/js/app.precompiled.js?v=202608081500" defer></script>
     <link rel="stylesheet" href="/static/css/styles.css?v=202607271016">
     <style>
         :root {
@@ -52,8 +52,43 @@
             --top-bar-height: 80px;
             --status-bar-height: 25px;
             --panel-border-color: #2a2a2a;
+            /* Theme (Preferences) — có thể override bằng data-theme trên <html> */
+            --sf-bg: #1e1e1e;
+            --sf-panel: #262626;
+            --sf-header: #2e2e2e;
+            --sf-border: #181818;
+            --sf-accent: #00ffcc;
         }
 
+        /* ── THEME presets (Tools → Preferences) ── */
+        html[data-theme="dark"] {
+            --sf-bg: #1e1e1e; --sf-panel: #262626; --sf-header: #2e2e2e; --sf-border: #181818; --sf-accent: #00ffcc;
+        }
+        html[data-theme="midnight"] {
+            --sf-bg: #0f172a; --sf-panel: #1e293b; --sf-header: #1e293b; --sf-border: #0f172a; --sf-accent: #38bdf8;
+        }
+        html[data-theme="forest"] {
+            --sf-bg: #111c15; --sf-panel: #1b2a1e; --sf-header: #1e2d21; --sf-border: #0c1510; --sf-accent: #34d399;
+        }
+        html[data-theme="violet"] {
+            --sf-bg: #170f26; --sf-panel: #221537; --sf-header: #251640; --sf-border: #110a1c; --sf-accent: #a78bfa;
+        }
+        html[data-theme="graphite"] {
+            --sf-bg: #18181b; --sf-panel: #232327; --sf-header: #27272a; --sf-border: #101012; --sf-accent: #e4e4e7;
+        }
+
+        /* Áp theme lên các vùng chính của app shell */
+        .daw-app-shell { background-color: var(--sf-bg) !important; }
+        .daw-panel { background-color: var(--sf-panel) !important; }
+        .daw-header { background-color: var(--sf-header) !important; }
+        body { background-color: var(--sf-bg) !important; }
+        ::-webkit-scrollbar-thumb { background: var(--sf-accent); }
+
+        /* ── BUTTON FONT SIZE (Tools → Preferences) ── */
+        html[data-btnfont="sm"] button { font-size: 10px !important; }
+        html[data-btnfont="md"] button { font-size: 12px !important; }
+        html[data-btnfont="lg"] button { font-size: 14px !important; }
+
         body {
             background-color: #1a1a1a;
             color: #c0c0c0;

wiki.md

@@ -1,3 +1,17 @@
+### [2026-08-08] FEAT: Menu Help (About + Hướng dẫn sử dụng) + Tools → Preferences (Theme/Language/Button font size)
+- **Tóm tắt thay đổi:** User yêu cầu 2 nhóm tính năng:
+  1. **Menu Help**: 
+     - `About SonicForge Studio...` → **AboutModal** mới: dev **Lộc Phạm**, email **tranloclqd@gmail.com**, version `1.0.0` (khớp tauri.conf.json), build Standalone (Tauri v2 + PyInstaller).
+     - `Hướng dẫn sử dụng...` → **HelpModal** mới: 8 mục hướng dẫn song ngữ (vi/en theo language preference): Bắt đầu nhanh, MIDI & ARM, Piano Roll, FX & Master, SoundFont & VST, AI, Lưu & Xuất, Phím tắt.
+  2. **Tools → Preferences...** → **PreferencesModal** mới quản lý:
+     - **Theme** (5 preset): dark (mặc định), midnight, forest, violet, graphite — áp qua `data-theme` trên `<html>` + CSS variables `--sf-bg/--sf-panel/--sf-header/--sf-border/--sf-accent` (thêm trong index.html `<style>`, override .daw-app-shell/.daw-panel/.daw-header/body/scrollbar).
+     - **Language**: vi/en — áp ngay cho HelpModal + PreferencesModal (menu chính giữ nguyên — app vốn song ngữ lẫn lộn).
+     - **Button font size**: sm/md/lg — áp qua `data-btnfont` trên `<html>` + CSS `html[data-btnfont=...] button { font-size: ... !important }`.
+  3. **Lưu trữ**: localStorage `sf_prefs` + server `/api/v1/user/preferences` (window.SonicAPI.getPreferences/savePreferences — endpoint đã có sẵn). Load server prefs khi khởi động.
+- **Các file ảnh hưởng:** `app/static/js/app.jsx` (AboutModal/HelpModal/PreferencesModal mới + state prefs + menu Tools/Help + render 3 modal), `app/static/js/app.precompiled.js` (rebuild), `app/templates/index.html` (CSS theme + data-btnfont + bump v=202608081500)
+- **Ghi chú/Test (nếu có):** BUILD OK 1123418 bytes, node --check OK, pytest 86 passed. Verify serve: index 200, precompiled 200, bundle chứa đủ "Hướng dẫn sử dụng", "tranloclqd@gmail.com", "data-btnfont", "Preferences". Lưu ý: button font size dùng !important nên override cả text-xs của Tailwind — đúng ý "đổi cỡ chữ button" nhưng có thể làm một số nút hơi to/nhỏ so với thiết kế gốc.
+
+---
 ### [2026-08-08] FIX: VU meter giữ animation đúng TRƯỜNG ĐỘ âm thanh khi ARM + nhấn/giữ phím MIDI keyboard
 - **Tóm tắt thay đổi:** User yêu cầu: bật ARM + nhấn phím MIDI keyboard preview — khi âm CÒN PLAY thì VU meter phải còn animate cho đúng trường độ âm thanh. Trước đây: note-on → `triggerMidiVuActivity` set peak → VU tick decay 0.75/frame → VU tắt sau ~0.5s DÙ âm còn kêu (note dài 60000ms, chỉ tắt khi note-off). Root cause: VU tick decay theo thời gian, không biết note đang giữ. Fix:
   1. **`heldMidiNotesRef`** (mới): đếm số note MIDI đang GIỮ per-track (ARM + keyboard live). Note-on → tăng counter (cả nhánh armed sub-tab PIANO_ROLL lẫn armed main track); note-off → giảm, về 0 thì xóa.