fix(minapps): ensure Region selector has default value for upgraded users

- Add migration 194 to initialize minAppRegion setting to auto
- Add defensive default value in RegionSelector component

Fixes: Region selector showing placeholder instead of default value

Author: GeorgeDong32

src/renderer/src/pages/minapps/MiniappSettings/MiniAppSettings.tsx

@@ -24,11 +24,11 @@ import MiniAppIconsManager from './MiniAppIconsManager'
 // 默认小程序缓存数量
 const DEFAULT_MAX_KEEPALIVE = 3
 
-// 地区选择器组件
+// Region selector component with defensive default value
 const RegionSelector: FC = () => {
   const { t } = useTranslation()
   const dispatch = useAppDispatch()
-  const minAppRegion = useAppSelector((state: RootState) => state.settings.minAppRegion)
+  const minAppRegion = useAppSelector((state: RootState) => state.settings.minAppRegion) ?? 'auto'
 
   const onMinAppRegionChange = (value: MinAppRegionFilter) => {
     dispatch(setMinAppRegion(value))

src/renderer/src/store/migrate.ts

@@ -3184,6 +3184,8 @@ const migrateConfig = {
           assistant.defaultModel = qwen3Next80BModel
         }
       })
+      // Initialize mini app region filter setting
+      state.settings.minAppRegion ??= 'auto'
       return state
     } catch (error) {
       logger.error('migrate 194 error', error as Error)