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/Cargo.toml

@@ -14,7 +14,7 @@ crate-type = ["staticlib", "cdylib", "rlib"]
 tauri-build = { version = "2", features = [] }
 
 [dependencies]
-tauri = { version = "2", features = ["tray-icon"] }
+tauri = { version = "2", features = ["macos-private-api", "tray-icon"] }
 tauri-plugin-shell = "2"
 tauri-plugin-fs = "2"
 tauri-plugin-dialog = "2"