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/proxy.ts

@@ -0,0 +1,9 @@
+import api from './client';
+import type { ProxyConfig, ProxyTestResult } from './types';
+
+export const proxyApi = {
+  get: () => api.get<ProxyConfig, ProxyConfig>('/proxy'),
+  update: (data: ProxyConfig) => api.put<ProxyConfig, ProxyConfig>('/proxy', data),
+  test: () => api.post<ProxyTestResult, ProxyTestResult>('/proxy/test'),
+  testWhitelist: () => api.post<ProxyTestResult, ProxyTestResult>('/proxy/whitelist/test'),
+};