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

src-tauri/capabilities/default.json

@@ -3,5 +3,5 @@
   "identifier": "default",
   "description": "Default capability for the main window",
   "windows": ["main"],
-  "permissions": ["core:default"]
+  "permissions": ["core:default", "dialog:default"]
 }