feat: 添加自定义模型路径配置功能

后端变更:
- src/app/commands.rs: 新增 select_model_file 命令，使用 Tauri dialog 打开文件选择器
- src/app/mod.rs: 注册 select_model_file 命令到 invoke_handler

前端变更:
- web/src/pages/SettingsPage.tsx:
  - 添加 modelPath 字段到 Settings 接口
  - 添加 handleSelectModel 函数处理文件选择
  - 添加模型路径配置 UI（输入框 + 选择按钮）
- web/src/App.css: 添加.model-path-selector 样式

功能说明:
- 用户可通过托盘菜单或设置页面选择自定义 ONNX 模型文件
- 支持 .onnx 扩展名过滤
- 模型路径保存在配置中，可选功能，留空时使用内置模型
- 设置保存后应用到 ASR 引擎

src/app/commands.rs

@@ -160,3 +160,26 @@ pub fn set_theme(theme: String, state: State<'_, AppState>) {
     let app_theme = AppTheme::from_str(&theme);
     state.set_theme(app_theme);
 }
+
+/// 选择模型文件
+#[tauri::command]
+pub async fn select_model_file(app: tauri::AppHandle) -> Result<String, String> {
+    use tauri_plugin_dialog::DialogExt;
+
+    let (tx, rx) = std::sync::mpsc::channel();
+
+    app.dialog()
+        .file()
+        .add_filter("ONNX Model", &["onnx"])
+        .pick_file(move |file_path| {
+            let result = match file_path {
+                Some(path) => Ok(path.to_string_lossy().to_string()),
+                None => Err("用户取消选择".to_string()),
+            };
+            let _ = tx.send(result);
+        });
+
+    rx.recv()
+        .map_err(|e| e.to_string())
+        .and_then(|r| r)
+}

src/app/mod.rs

@@ -45,6 +45,7 @@ pub fn run() -> Result<()> {
             commands::clear_history,
             commands::get_theme,
             commands::set_theme,
+            commands::select_model_file,
         ])
         .setup(|app| {
             info!("[设置] 初始化应用插件...");

web/src/App.css

@@ -299,3 +299,16 @@ body {
   background: var(--accent);
   color: var(--text-primary);
 }
+
+/* 模型路径选择器 */
+.model-path-selector {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  width: 100%;
+}
+
+.model-path-selector .input {
+  flex: 1;
+  min-width: 200px;
+}

web/src/pages/SettingsPage.tsx

@@ -13,6 +13,7 @@ interface Settings {
   hotkeyRecord: string
   hotkeyCopy: string
   hotkeyToggle: string
+  modelPath?: string
 }
 
 interface SettingsPageProps {
@@ -20,6 +21,12 @@ interface SettingsPageProps {
   onThemeChange: (theme: 'light' | 'dark' | 'system') => void
 }
 
+declare const window: Window & {
+  __TAURI__: {
+    invoke: (cmd: string, args?: Record<string, unknown>) => Promise<unknown>
+  }
+}
+
 export default function SettingsPage({ theme, onThemeChange }: SettingsPageProps) {
   const [settings, setSettings] = useState<Settings>({
     model: 'sensevoice-small',
@@ -63,11 +70,24 @@ export default function SettingsPage({ theme, onThemeChange }: SettingsPageProps
       historyKeepDays: 30,
       hotkeyRecord: 'Ctrl+Shift+R',
       hotkeyCopy: 'Ctrl+Shift+C',
-      hotkeyToggle: 'Ctrl+Shift+H'
+      hotkeyToggle: 'Ctrl+Shift+H',
+      modelPath: undefined
     })
     setModified(true)
   }
 
+  const handleSelectModel = async () => {
+    try {
+      const modelPath = await window.__TAURI__.invoke<string>('select_model_file')
+      if (modelPath) {
+        setSettings(prev => ({ ...prev, modelPath }))
+        setModified(true)
+      }
+    } catch (e) {
+      console.error('选择模型文件失败:', e)
+    }
+  }
+
   return (
     <div className="settings-page">
       <h1 className="page-title">设置</h1>
@@ -94,6 +114,27 @@ export default function SettingsPage({ theme, onThemeChange }: SettingsPageProps
             </select>
           </div>
 
+          <div className="setting-item">
+            <div>
+              <div className="setting-label">模型路径</div>
+              <div className="setting-description">自定义模型文件路径（可选，留空使用内置模型）</div>
+            </div>
+            <div className="model-path-selector">
+              <input
+                type="text"
+                className="input"
+                style={{ flex: 1, marginRight: '8px' }}
+                value={settings.modelPath || ''}
+                onChange={(e) => handleChange('modelPath', e.target.value)}
+                placeholder="选择自定义模型文件..."
+                readOnly
+              />
+              <button className="btn btn-secondary" onClick={handleSelectModel}>
+                选择文件
+              </button>
+            </div>
+          </div>
+
           <div className="setting-item">
             <div>
               <div className="setting-label">识别语言</div>