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

package.json

@@ -10,10 +10,12 @@
     "build:shared": "pnpm --filter @backspace/shared build",
     "build:server": "pnpm --filter @backspace/server build",
     "build:web": "pnpm --filter @backspace/web build",
-    "build": "pnpm --filter @backspace/shared build && pnpm --filter @backspace/server build & pnpm --filter @backspace/web build"
+    "build": "pnpm --filter @backspace/shared build && pnpm --filter @backspace/server build & pnpm --filter @backspace/web build",
+    "dev:desktop": "pnpm --filter @backspace/desktop dev",
+    "build:desktop": "pnpm --filter @backspace/desktop build"
   },
   "pnpm": {
-    "onlyBuiltDependencies": ["better-sqlite3", "esbuild", "sharp"]
+    "onlyBuiltDependencies": ["better-sqlite3", "esbuild", "electron", "sharp"]
   },
   "engines": {
     "node": ">=20.0.0",