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/ai-tools.tsx

@@ -311,7 +311,7 @@ export function AssetFactoryPage({ navigate }: { navigate: (page: Page) => void
             const img = taskImage[task.id];
             return (
               <article className="task-card history-card" key={task.id}>
-                <div className={`placeholder${img ? " has-img" : ""}`}>{img ? <img src={img} alt={typeLabel} /> : <span className="ph-frame">{task.id.slice(0, 4)}</span>}</div>
+                <div className={`placeholder${img ? " has-img" : ""}`}>{img ? <img src={img} alt={typeLabel} loading="lazy" decoding="async" /> : <span className="ph-frame">{task.id.slice(0, 4)}</span>}</div>
                 <div className="history-body">
                   <div className="history-name">{typeLabel}</div>
                   <div className="history-type">// {task.task_type}</div>
@@ -346,7 +346,7 @@ export function AssetFactoryPage({ navigate }: { navigate: (page: Page) => void
                     <td>
                       <div className="task-name-cell">
                         <div className={`placeholder task-thumb${img ? " has-img" : ""}`}>
-                          {img ? <img src={img} alt={typeLabel} /> : <span className="ph-frame">{task.id.slice(0, 4)}</span>}
+                          {img ? <img src={img} alt={typeLabel} loading="lazy" decoding="async" /> : <span className="ph-frame">{task.id.slice(0, 4)}</span>}
                         </div>
                         <div>
                           <div className="task-name">{typeLabel}</div>