fix(provider): persist endpoint auto-select state (#611)

- Add endpointAutoSelect field to ProviderMeta for persistence
- Lift autoSelect state from EndpointSpeedTest to ProviderForm
- Save auto-select preference when provider is saved
- Restore preference when editing existing provider

Fixes https://github.com/farion1231/cc-switch/issues/589

src/types.ts

@@ -92,6 +92,8 @@ export interface ProviderMeta {
   custom_endpoints?: Record<string, CustomEndpoint>;
   // 用量查询脚本配置
   usage_script?: UsageScript;
+  // 请求地址管理：测速后自动选择最佳端点
+  endpointAutoSelect?: boolean;
   // 是否为官方合作伙伴
   isPartner?: boolean;
   // 合作伙伴促销 key（用于后端识别 PackyCode 等）