perf(core): Wave 0 性能根因 — 连接复用/视频轮询脏检查/图懒加载/隐藏tab停轮询

- settings/base.py: MySQL 加 CONN_MAX_AGE=300 + 健康检查 + connect_timeout=5
  (development/production 共用,production 经 from .base import * 继承);development 去重
- App.tsx pollVideosQuiet: 收尾 setProjectDetail 改 JSON 脏检查,在途段未变化时
  跳过 setState,整棵管线不再每 5 秒空重渲染(纯前端,不碰生成业务)
- ai-tools.tsx: 任务历史网格+列表两处 img 补 loading=lazy/decoding=async
- pipeline.tsx: 审核(8s)+在途资产(4s)纯读轮询加 document.hidden 守卫
  (视频5s轮询驱动生成,保守不加;详见进度文档)

验证: tsc 0 · django check 0 · 14 路由 headless boot 0 报错 · 登录 726ms 无假延迟无邮箱

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

core/frontend/src/routes/pipeline.tsx

@@ -802,6 +802,7 @@ export function PipelinePage(props: {
     let sawProcessing = false;
     let timer = 0;
     const tick = async () => {
+      if (document.hidden) return; // 标签页切走时不空跑审核轮询(纯读,回前台自然恢复)
       const r = await api.pollReviews(project.id).catch(() => null);
       if (!alive) return;
       const map = (r?.reviews || {}) as Record<string, string>;
@@ -2078,6 +2079,7 @@ export function PipelinePage(props: {
     let stopped = false;
     let timer = 0;
     const tick = async () => {
+      if (document.hidden) { if (!stopped) timer = window.setTimeout(tick, 4000); return; } // 后台不空跑(纯读),保留心跳回前台即恢复
       try {
         const res = await api.pendingAssets(project.id);
         if (stopped) return;