feat: Electron desktop app + onboarding wizard

- electron/main.ts: native window, tray icon, gateway detection, IPC handlers
- electron/preload.ts: secure IPC bridge for renderer
- electron/onboarding/index.html: 3-step setup wizard
  - Connect Existing Gateway (auto-detect localhost:18789)
  - Local New Install (npm install -g openclaw in background)
  - Cloud (waitlist for managed hosting)
- electron-builder.config.js: Mac/Win/Linux packaging, GitHub auto-update
- package.json: electron scripts (electron:dev, electron:build:mac/win)

package.json

@@ -11,6 +11,7 @@
   "homepage": "https://clawsuite.io",
   "private": true,
   "type": "module",
+  "main": "electron/main.js",
   "scripts": {
     "dev": "vite dev --port 3000",
     "build": "vite build",
@@ -19,6 +20,10 @@
     "lint": "eslint",
     "format": "prettier",
     "check": "prettier --write . && eslint --fix",
+    "electron:dev": "NODE_ENV=development electron .",
+    "electron:build": "npm run build && electron-builder --config electron-builder.config.js",
+    "electron:build:mac": "npm run build && electron-builder --mac --config electron-builder.config.js",
+    "electron:build:win": "npm run build && electron-builder --win --config electron-builder.config.js",
     "beta:reset-state": "bash scripts/beta/reset_local_state.sh",
     "beta:export-diagnostics": "bash scripts/beta/export_diagnostics_and_scan.sh"
   },