feat(export): stop transport khi export offline + check file export khong cam (peak < -60dB -> canh bao)

app/static/js/app.jsx

@@ -27935,6 +27935,9 @@ const App = () => {
 
   // ── Server-side Export ──
   const triggerWavExport = async () => {
+    // Stop transport ngay khi bắt đầu export offline → tắt âm thanh đang phát.
+    try { if (typeof stopAllPlayback === 'function') stopAllPlayback(); } catch (e) { }
+    try { if (window.SonicSF && window.SonicSF.stopAllNotes) window.SonicSF.stopAllNotes(); } catch (e) { }
     // Realtime UNCHECKED → export OFFLINE thuần (server-side nếu connected, fallback client).
     // MIDI không render được trong OfflineAudioContext: nếu project có MIDI items mà
     // cache preview chưa đủ → file xuất có thể thiếu âm MIDI. Cảnh báo, vẫn xuất offline.
@@ -28669,11 +28672,13 @@ const App = () => {
       writeString(36, 'data');
       view.setUint32(40, exportLength * bytesPerSample * numExportCh, true);
       let offset = 44;
+      let peak = 0;
       for (let i = 0; i < exportLength; i++) {
         if ((i & 0x3FFF) === 0) setExportProgress(60 + Math.round((i / Math.max(1, exportLength)) * 32));
         for (let ch = 0; ch < numExportCh; ch++) {
           const chData = renderedBuffer.getChannelData(ch);
           const sample = Math.max(-1, Math.min(1, chData[i]));
+          if (Math.abs(sample) > peak) peak = Math.abs(sample);
           if (bitDepth === 8) {
             view.setUint8(offset, Math.floor((sample + 1.0) * 127.5));
           } else if (bitDepth === 16) {
@@ -28689,6 +28694,9 @@ const App = () => {
           offset += bytesPerSample;
         }
       }
+      if (peak < 0.001) {
+        showToast("Cảnh báo: file export gần như CÂM (không có tín hiệu âm) — kiểm tra nguồn track / MIDI cache preview.", "warning");
+      }
       const blob = new Blob([view], {
         type: 'audio/wav'
       });

app/templates/index.html

@@ -51,7 +51,7 @@
     <script src="/static/js/services/promptTemplateManager.js?v=202607281039"></script>
     <script src="/static/js/services/undoRedoEngine.js?v=202607290941"></script>
     <script src="/static/js/services/chordTheory.js?v=202608211300"></script>
-    <script src="/static/js/app.precompiled.js?v=202608232345" defer></script>
+    <script src="/static/js/app.precompiled.js?v=202608240010" defer></script>
     <link rel="stylesheet" href="/static/css/styles.css?v=202607271016">
     <style>
         :root {