fix(api): disable HTTP keep-alive to prevent ECONNRESET on reused sockets

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/api/axios-client.ts

@@ -1,4 +1,5 @@
 import axios, { AxiosRequestConfig, AxiosResponse, isAxiosError } from 'axios';
+import http from 'http';
 import { mockData, type MockApiResponse } from './mock';
 import { API_BASE_URL, DOCUMENT_URL } from '../config/api-config';
 import { toastService } from '../components/ui/Toast';
@@ -41,7 +42,9 @@ const axiosInstance = axios.create({
   headers: {
     'Content-Type': 'application/json',
     'Accept': 'application/json'
-  }
+  },
+  // 修复 ECONNRESET: 禁用 keep-alive 复用，避免后端关闭空闲连接后前端仍复用导致 reset
+  httpAgent: new http.Agent({ keepAlive: false }),
 });
 
 // 请求白名单 - 这些接口不需要添加 Authorization 头