feat(desktop): 添加悬浮球 Quick Ask 功能

- 实现浅灰色玻璃拟态悬浮球，带机器人头图标
- 支持点击展开对话框，淡入淡出动画
- 支持窗口拖拽，区分点击和拖拽操作
- macOS 透明窗口支持 (macOSPrivateApi)
- 悬浮球 hover 放大效果，不溢出窗口
- 添加系统托盘 Toggle Quick Ask 菜单

packages/desktop/src-tauri/tauri.conf.json

@@ -11,8 +11,10 @@
   },
   "app": {
     "withGlobalTauri": true,
+    "macOSPrivateApi": true,
     "windows": [
       {
+        "label": "main",
         "title": "AI Assistant",
         "width": 1200,
         "height": 800,
@@ -21,13 +23,29 @@
         "resizable": true,
         "fullscreen": false,
         "center": true
+      },
+      {
+        "label": "floating",
+        "title": "",
+        "url": "/floating.html",
+        "width": 60,
+        "height": 60,
+        "minWidth": 60,
+        "minHeight": 60,
+        "resizable": false,
+        "decorations": false,
+        "transparent": true,
+        "shadow": false,
+        "alwaysOnTop": true,
+        "visible": true,
+        "skipTaskbar": true
       }
     ],
     "security": {
       "csp": "default-src 'self'; connect-src 'self' http://localhost:* ws://localhost:* http://127.0.0.1:* ws://127.0.0.1:*; script-src 'self' 'unsafe-inline' 'unsafe-eval'; style-src 'self' 'unsafe-inline'"
     },
     "trayIcon": {
-      "iconPath": "icons/icon.png",
+      "iconPath": "icons/32x32.png",
       "iconAsTemplate": true
     }
   },