refactor(desktop): 替换 WebUI 为 Electron + electron-vite 桌面壳方案

- 使用 electron-vite 构建 main/preload，electron-builder 打包分发
- main process: dev 模式直连 localhost:3000，生产模式 spawn sidecar binary
- 添加 loading 页面，server 就绪前显示加载动画
- 更新 catalog 依赖: electron, electron-vite, electron-builder
- 移除 @webui-dev/bun-webui 依赖

apps/desktop/package.json

@@ -3,16 +3,21 @@
   "version": "1.0.0",
   "private": true,
   "type": "module",
+  "main": "out/main/index.js",
   "scripts": {
-    "dev": "bun src/bun/index.ts",
+    "dev": "electron-vite dev",
+    "build": "electron-vite build",
+    "build:win": "electron-vite build && electron-builder --win --config",
+    "build:mac": "electron-vite build && electron-builder --mac --config",
+    "build:linux": "electron-vite build && electron-builder --linux --config",
     "fix": "biome check --write",
     "typecheck": "tsc --noEmit"
   },
-  "dependencies": {
-    "@webui-dev/bun-webui": "catalog:"
-  },
   "devDependencies": {
     "@furtherverse/tsconfig": "workspace:*",
-    "@types/bun": "catalog:"
+    "@types/node": "catalog:",
+    "electron": "catalog:",
+    "electron-builder": "catalog:",
+    "electron-vite": "catalog:"
   }
 }