feat: Provider 异步删除、可配置密码策略、Hub 超时优化及多项改进

- 新增 Provider 异步删除任务系统，后台分阶段删除子资源并清理残留引用
- 新增可配置密码策略等级（weak/medium/strong），支持系统设置面板调整
- aether-hub 升级至 0.1.4，idle timeout 支持禁用（设为 0），worker 默认超时调整为 120s
- OAuth 手动续期增加 Redis 分布式锁，防止并发刷新冲突
- ProxyNode 心跳检测改为 asyncio.to_thread，避免阻塞事件循环
- 删除 ModelMultiSelect 和 useInvalidModels，MultiSelect 组件通用化
- 明确 allowed_providers/allowed_api_formats 的 NULL 与空数组语义
- 前端 StandaloneKeyFormDialog、UserFormDialog 等多处 UI 优化
- 新增 Alembic 迁移脚本清理 Provider 删除后的残留引用
- 补充相关测试用例

frontend/src/api/auth.ts

@@ -81,6 +81,7 @@ export interface RegistrationSettingsResponse {
   enable_registration: boolean
   require_email_verification: boolean
   email_configured: boolean
+  password_policy_level: string
 }
 
 export interface AuthSettingsResponse {

frontend/src/api/endpoints/providers.ts

@@ -114,8 +114,36 @@ export async function createProvider(
 /**
  * 删除 Provider
  */
-export async function deleteProvider(providerId: string): Promise<{ message: string }> {
-  const response = await client.delete(`/api/admin/providers/${providerId}`)
+export interface ProviderDeleteSubmitResponse {
+  task_id: string
+  status: string
+  message: string
+}
+
+export interface ProviderDeleteTaskResponse {
+  task_id: string
+  provider_id: string
+  status: string
+  stage: string
+  total_keys: number
+  deleted_keys: number
+  total_endpoints: number
+  deleted_endpoints: number
+  message: string
+}
+
+export async function deleteProvider(providerId: string): Promise<ProviderDeleteSubmitResponse> {
+  const response = await client.delete<ProviderDeleteSubmitResponse>(`/api/admin/providers/${providerId}`)
+  return response.data
+}
+
+export async function getProviderDeleteTask(
+  providerId: string,
+  taskId: string,
+): Promise<ProviderDeleteTaskResponse> {
+  const response = await client.get<ProviderDeleteTaskResponse>(
+    `/api/admin/providers/${providerId}/delete-task/${taskId}`,
+  )
   return response.data
 }