feat(engine): 优化 Vosk 字幕引擎支持

- 实现文件夹选择功能，用于选择 Vosk 模型路径
- 在 EngineControl 组件中添加模型路径选择按钮和相关提示
- 在 EngineStatus 组件中增加对空模型路径的检查和错误提示

src/main/ControlWindow.ts

@@ -1,4 +1,4 @@
-import { shell, BrowserWindow, ipcMain, nativeTheme } from 'electron'
+import { shell, BrowserWindow, ipcMain, nativeTheme, dialog } from 'electron'
 import path from 'path'
 import { is } from '@electron-toolkit/utils'
 import icon from '../../build/icon.png?asset'
@@ -72,6 +72,15 @@ class ControlWindow {
       return allConfig.uiTheme
     })
 
+    ipcMain.handle('control.folder.select', async () => {
+      const result = await dialog.showOpenDialog({
+        properties: ['openDirectory']
+      });
+
+      if (result.canceled) return "";
+      return result.filePaths[0];
+    })
+
     ipcMain.on('control.uiLanguage.change', (_, args) => {
       allConfig.uiLanguage = args
       if(captionWindow.window){