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

packages/desktop/package.json

@@ -6,11 +6,12 @@
   "scripts": {
     "build:ts": "tsc",
     "dev": "tsc && electron .",
+    "prebuild": "mkdir -p build && cp ../web/public/icons/icon-512.png build/icon.png 2>/dev/null || true",
     "build": "tsc && electron-builder",
     "clean": "rm -rf dist dist-electron"
   },
   "dependencies": {
-    "electron-is-dev": "^3.0.1"
+    "electron-updater": "^6.3.0"
   },
   "devDependencies": {
     "electron": "^33.2.0",