Remove Carla native VSTi bridge entirely

Drop Carla integration across frontend and backend:
- plugins.py: remove /carla-midi, /carla-status, /carla-stop, /open-in-carla,
  /carla-play-notes endpoints and Carla process management
- runtime.py: remove find_carla / _carla_* helpers, detect and capabilities
- app.jsx: remove Carla bridge UI, SonicCarlaMidi routing, shouldRouteCarla
  guards, VST row Carla button and preset fallback
- system.py: remove /carla-path
- Keep audio path unchanged (tracks -> masterBus -> output -> analyser),
  directOut only for offline render

Build frontend, tests pass (124 passed).

app/static/js/services/api.js

@@ -73,18 +73,6 @@ window.API_BASE_URL = (window.API_BASE_URL || window.location.origin).replace(/\
         // Runtime capabilities — frontend gọi lúc boot để biết môi trường
         // (desktop Windows / docker headless) và bật/tắt tính năng
         getCapabilities: () => apiRequest('/api/v1/system/capabilities', { method: 'GET' }),
-        // Định vị Carla.exe (bản portable zip không cài đặt/PATH) — lưu config
-        setCarlaPath: (path) => apiRequest('/api/v1/system/carla-path', { method: 'POST', body: JSON.stringify({ carla_path: path }) }),
-        // Mở native GUI VSTi trong Carla (chỉ khi runtime=desktop + có Carla local)
-        openInCarla: (pluginName, pluginPath) => apiRequest('/api/v1/plugins/open-in-carla', { method: 'POST', body: JSON.stringify({ plugin_name: pluginName, plugin_path: pluginPath }) }),
-        // Unload Carla bridge: tắt mọi note đang ngân + terminate tiến trình Carla
-        // do app spawn (gọi khi track chuyển từ VSTi sang instrument soundfont)
-        stopCarla: () => apiRequest('/api/v1/plugins/carla-stop', { method: 'POST', body: JSON.stringify({}) }),
-        // Kiểm tra Carla còn sống không (app-spawn) + cổng OSC — quyết định
-        // route MIDI item exclusive qua Carla hay fallback FluidSynth
-        carlaStatus: () => apiRequest('/api/v1/plugins/carla-status', { method: 'GET' }),
-        // Gửi MIDI note (track ARM → Carla OSC) để preview VSTi realtime
-        carlaMidi: (payload) => apiRequest('/api/v1/plugins/carla-midi', { method: 'POST', body: JSON.stringify(payload) }),
         // Quick-render preview VSTi (âm thật = âm export, cùng code path)
         previewInstrument: (payload) => apiRequest('/api/v1/plugins/preview', { method: 'POST', body: JSON.stringify(payload) }),
         // Render MIDI notes → WAV bằng VSTi (pedalboard, âm thật) — trả file_id
@@ -99,10 +87,7 @@ window.API_BASE_URL = (window.API_BASE_URL || window.location.origin).replace(/\
         // Mở native GUI của VST FX (mastering chain / FX rack) qua bridge
         openFxGui: (payload) => apiRequest('/api/v1/plugins/fx-gui', { method: 'POST', body: JSON.stringify(payload) }),
         soundfontRender: (payload) => apiRequest('/api/v1/plugins/soundfont-render', { method: 'POST', body: JSON.stringify(payload) }),
-        // Phát dãy MIDI notes realtime qua Carla bridge (OSC) — preview khi
-        // pedalboard không render được plugin (VD VST2)
-        carlaPlayNotes: (payload) => apiRequest('/api/v1/plugins/carla-play-notes', { method: 'POST', body: JSON.stringify(payload) }),
-        // Thư viện preset VST3 (.vstpreset) — cầu nối Carla → pedalboard
+        // Thư viện preset VST3 (.vstpreset) — cầu nối preset → pedalboard
         listPresets: () => apiRequest('/api/v1/presets', { method: 'GET' }),
         uploadPreset: (file, pluginHint) => {
             const fd = new FormData();