feat(ai): 后台 AI 链路改走 HTTP 流式，WS 地址与心跳收敛到 utils

写作 / 图片 / 大纲 / 稿件四条链路用普通 POST 时，生成期间链路上零字节，
会被 60s 空闲超时掐成 504（出图实测 58s 断开）。后端已给每条链路开
/stream（SSE，每 15s 一帧心跳），这里改成消费它。

- 新增 utils/ai-stream.ts：SSE 帧解析 + 末帧 {type:'final', result} 拆包；
  runCreativeAssistantStream / runManuscriptGenStream 对外仍返回原来的 data，
  页面渲染逻辑不动
- 新增 utils/chat-socket.ts：buildWebSocketUrl 统一拼 /api/chat/{userId}
  （网关只放行 /api 前缀），attachHeartbeat 每 25s 发 ping 顶住代理空闲超时
- chatgpt 对话先试 WebSocket，握手失败落 /ai/chat/message/stream，
  帧内容与 WS 完全一致，处理函数直接复用
- 四个页面删掉各自重复的 buildWebSocketUrl，统一从 utils 引入

src/views/gxmu/WXXZXForm/components/docValidate.vue

@@ -146,7 +146,7 @@
   import ByteMdViewer from '@/components/ByteMdViewer/index.vue';
   import { reviewWxxzxProjectBookQuality } from '@/api/gxmu/wxxzx-form';
   import { stopMessage } from '@/api/oa/chatgpt';
-  import { API_BASE_URL } from '@/config/setting';
+  import { attachHeartbeat, buildWebSocketUrl } from '@/utils/chat-socket';
   import { useUserStore } from '@/store/modules/user';
   import { copyText } from '@/utils/common';
   import type { WxxzxProjectQualityReviewResult } from '@/api/gxmu/wxxzx-form/model';
@@ -249,17 +249,6 @@
     });
   };
 
-  const buildWebSocketUrl = (userId: number) => {
-    if (/^https?:\/\//.test(API_BASE_URL)) {
-      const url = new URL(API_BASE_URL);
-      url.protocol = url.protocol === 'https:' ? 'wss:' : 'ws:';
-      url.pathname = url.pathname.replace(/\/api\/?$/, '');
-      return `${url.toString().replace(/\/$/, '')}/chat/${userId}`;
-    }
-    const protocol = window.location.protocol === 'https:' ? 'wss:' : 'ws:';
-    return `${protocol}//${window.location.host}/chat/${userId}`;
-  };
-
   const clearStreamResolver = () => {
     streamResolverRef.value = null;
   };
@@ -402,6 +391,10 @@
     const connectPromise = new Promise<void>((resolve, reject) => {
       let settled = false;
       const socket = new WebSocket(buildWebSocketUrl(userId));
+      socket.onopen = () => {
+        // 握手成功后再挂心跳：连接没建起来时发出去只会失败
+        attachHeartbeat(socket);
+      };
       cleanupPending = () => {
         if (wsConnectPromiseRef.value === connectPromise) {
           wsConnectPromiseRef.value = null;