FEAT: Plugin Manager folder picker + scan dirs (Windows/macOS), docker .env paths, status bar adaptive tips, DSP Tool vao sub-tab audioclip

- Plugins Manager (Tools menu): Browse folder (Tauri dialog + fallback paste path), Save & Scan VST/SoundFont dirs -> plugin_dirs.json (user override, env la base)
- Docker: VST_DIR/SOUNDFONT_DIR/PIANOBK_DIR tu .env/docker-compose mount vao container + env cho engine/celery
- Status bar: bo label 'Scroll: Zoom' -> Adaptive tips (prHint + fallback text)
- DSP Tool: move vao SUB-TAB editor audioclip (Phase Inv / Swap L/R / Reverse + apply vung chon/ca clip)
- Tauri: them tauri-plugin-dialog + dialog:default permission cho folder picker

app/static/js/services/api.js

@@ -64,6 +64,9 @@ window.API_BASE_URL = window.API_BASE_URL || window.location.origin;
         savePreferences: (prefs) => apiRequest('/api/v1/user/preferences', { method: 'POST', body: JSON.stringify({ preferences: prefs }) }),
 
         listPlugins: () => apiRequest('/api/v1/plugins/available', { method: 'GET' }),
+        getPluginDirs: () => apiRequest('/api/v1/plugins/dirs', { method: 'GET' }),
+        savePluginDirs: (dirs) => apiRequest('/api/v1/plugins/dirs', { method: 'POST', body: JSON.stringify(dirs) }),
+        scanPluginDirs: () => apiRequest('/api/v1/plugins/scan', { method: 'POST' }),
         getSoundfontCatalog: () => apiRequest('/api/v1/plugins/soundfonts/catalog', { method: 'GET' }),
         listDefaultSoundfonts: () => apiRequest('/api/v1/plugins/default-soundfonts', { method: 'GET' }),
         listSoundfontInstruments: (sfId) => apiRequest(`/api/v1/plugins/soundfont-instruments/${sfId}`, { method: 'GET' }),