feat: add config directory override support for WSL

- Add persistent app settings with custom Claude Code and Codex config directories
- Add config directory override UI in settings modal with manual input, browse, and reset options
- Integrate tauri-plugin-dialog for native directory picker
- Support WSL and other special environments where config paths need manual specification

Changes:
- settings.rs: Implement settings load/save and directory override logic
- SettingsModal: Add config directory override UI components
- API: Add get_config_dir and pick_directory commands

src/types.ts

@@ -24,4 +24,8 @@ export interface AppConfig {
 export interface Settings {
   // 是否在系统托盘（macOS 菜单栏）显示图标
   showInTray: boolean;
+  // 覆盖 Claude Code 配置目录（可选）
+  claudeConfigDir?: string;
+  // 覆盖 Codex 配置目录（可选）
+  codexConfigDir?: string;
 }