fix: 修复proxy_service和account_service中不当的顶层import

- proxy_service.py: 将requests和WhitelistManager改为函数内延迟import，
  避免启动时加载不需要的依赖；移除未使用的get_exit_ip_via_proxy导入
- account_service.py: 移除未使用的func、joinedload、AuditLog、
  user_has_permission顶层导入

web/frontend/src/api/users.ts

@@ -0,0 +1,12 @@
+import api from './client';
+import type { MessageResponse, PermissionsListResult, UserInfo } from './types';
+
+export const userApi = {
+  list: () => api.get<UserInfo[], UserInfo[]>('/users'),
+  create: (data: { username: string; password: string; role: string; remark?: string }) =>
+    api.post<UserInfo, UserInfo>('/users', data),
+  update: (id: number, data: { password?: string; role?: string; is_active?: boolean; remark?: string; custom_permissions?: string[] | null }) =>
+    api.put<UserInfo, UserInfo>(`/users/${id}`, data),
+  delete: (id: number) => api.delete<MessageResponse, MessageResponse>(`/users/${id}`),
+  listPermissions: () => api.get<PermissionsListResult, PermissionsListResult>('/users/permissions/list'),
+};