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/oa/chatgpt/index.vue

@@ -389,15 +389,14 @@ import type { AiChatHistory } from "@/api/ai/aiChatHistory/model";
 import { listAiChatList, removeAiChatList } from "@/api/ai/aiChatList";
 import type { AiChatList } from "@/api/ai/aiChatList/model";
 import { sendMessage, stopMessage } from "@/api/oa/chatgpt";
-import { manuscriptGen } from "@/api/ai/manuscriptGen";
+import { runCreativeAssistantStream, runManuscriptGenStream, streamChatMessage } from "@/utils/ai-stream";
 import {
     WRITING_DOC_TYPE_FREE,
     WRITING_DOC_TYPE_OPTIONS,
     WRITING_EVENT_TYPE_OPTIONS,
     WRITING_WORD_COUNT_OPTIONS
 } from "./writing-params";
-import { creativeAssistant } from "@/api/ai/creativeAssistant";
-import { API_BASE_URL } from "@/config/setting";
+import { attachHeartbeat, buildWebSocketUrl } from "@/utils/chat-socket";
 import type { Menu } from "@/api/system/menu/model";
 import { useUserStore } from "@/store/modules/user";
 import { logout } from "@/utils/page-tab-util";
@@ -785,17 +784,6 @@ const findFirstChildMenuPath = (menus: AuthorityTreeItem[]) => {
     return "";
 };
 
-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 formatHistoryMessages = (list: AiChatHistory[]) => {
     const result: ChatMessageItem[] = [];
     [...list]
@@ -972,6 +960,7 @@ const connectWebSocket = async () => {
             }
         };
         socket.onopen = () => {
+          attachHeartbeat(socket);
             wsConnected.value = false;
         };
         socket.onmessage = (event) => {
@@ -1335,7 +1324,8 @@ const sendModeMessage = async (
         }
     };
     if (activeChatMode.value === "writing") {
-        const result = await manuscriptGen(buildWritingPayload(query), { signal });
+        // 稿件生成同样会被链路的 60s 空闲超时掐掉，改走流式（正文边推边显示）
+        const result = await runManuscriptGenStream(buildWritingPayload(query), signal);
         if (typeof (result as any)?.taskId === "string") {
             currentTaskId.value = (result as any).taskId;
         }
@@ -1343,7 +1333,8 @@ const sendModeMessage = async (
         return;
     }
     if (activeChatMode.value === "image") {
-        const result = await creativeAssistant(buildImagePayload(query), { signal });
+        // 出图中途零字节，普通 POST 会被网关按 60s 空闲超时掐成 504，改走流式
+        const result = await runCreativeAssistantStream(buildImagePayload(query), signal);
         if (typeof (result as any)?.taskId === "string") {
             currentTaskId.value = (result as any).taskId;
         }
@@ -1471,13 +1462,24 @@ const onSend = async () => {
         content.value = "";
         scrollToBottom();
         if (activeChatMode.value === "chat") {
-            await connectWebSocket();
-            await sendMessage({
+            // 先试 WebSocket；生产网关在 /api 前丢 Upgrade 头，握手必然失败，
+            // 这时落到 HTTP 流式端点，帧内容与 WS 完全一致，解析逻辑不用改
+            const payload = {
                 query,
                 conversationId: activeConversationId.value
-            }, {
-                signal: abortController.signal
-            });
+            };
+            const viaSocket = await connectWebSocket()
+                .then(() => true)
+                .catch(() => false);
+            if (viaSocket) {
+                await sendMessage(payload, { signal: abortController.signal });
+            } else {
+                await streamChatMessage(
+                    payload as Record<string, unknown>,
+                    (raw) => void handleSocketMessage(raw),
+                    abortController.signal
+                );
+            }
         } else {
             await sendModeMessage(query, assistantId, abortController.signal);
             streamingMessageId.value = undefined;