feat: Electron desktop app — hardening, IPC bridge, and dev launch fixes

- Dev/prod URL auto-detection (Vite 5173 in dev, server 3000 in prod)
- Typed IPC bridge via preload (notifications, badge, window controls, updates, deep links)
- Native OS notifications via NotificationController with window focus suppression
- Auto-update via electron-updater with UpdateToast UI
- Deep linking (backspace:// protocol) for macOS and Windows/Linux
- Window state persistence (position, size, maximize across restarts)
- Tray icon with graceful fallback when icon asset missing
- Suppress PWA service worker polling/reloads inside Electron
- Platform detection layer (isElectron, getElectronAPI)
- Root workspace scripts (dev:desktop, build:desktop)
- Document BACKSPACE_URL and BACKSPACE_UPDATE_URL env vars

.env.example

@@ -25,6 +25,13 @@ LIVEKIT_URL=
 LIVEKIT_API_KEY=
 LIVEKIT_API_SECRET=
 
+# ─── Desktop App (Electron) ───────────────────────────────
+# Override the URL that the desktop app loads (auto-detects in dev/prod)
+# BACKSPACE_URL=https://my-instance.com
+
+# Auto-update server URL for electron-updater (optional)
+# BACKSPACE_UPDATE_URL=https://releases.example.com
+
 # ─── Docker Compose ────────────────────────────────────────
 # Uncomment to enable the LiveKit service:
 # COMPOSE_PROFILES=voice