fix(web): align playground chat layout

apps/web/src/components/layout/AppShell.tsx

@@ -1,11 +1,12 @@
 import type { ReactNode } from 'react';
-import { BookOpen, Boxes, Home, RefreshCw, ShieldCheck, UserCircle } from 'lucide-react';
+import { BookOpen, Boxes, Home, RefreshCw, ShieldCheck, Sparkles, UserCircle } from 'lucide-react';
 import type { HealthResponse } from '../../api';
 import type { LoadState, PageKey } from '../../types';
 import { Button, Badge } from '../ui';
 
 const navItems: Array<{ key: PageKey; label: string; icon: ReactNode }> = [
   { key: 'home', label: '首页', icon: <Home size={17} /> },
+  { key: 'playground', label: '在线测试', icon: <Sparkles size={17} /> },
   { key: 'models', label: '模型', icon: <Boxes size={17} /> },
   { key: 'workspace', label: '用户工作台', icon: <UserCircle size={17} /> },
   { key: 'admin', label: '管理工作台', icon: <ShieldCheck size={17} /> },
@@ -24,7 +25,7 @@ export function AppShell(props: {
   onSignOut: () => void;
 }) {
   return (
-    <div className="appShell">
+    <div className="appShell" data-page={props.activePage}>
       <header className="appTopbar">
         <div className="brandBlock">
           <div className="brandMark">AI</div>
@@ -72,7 +73,7 @@ export function AppShell(props: {
       </header>
 
       <div className="workspaceShell">
-        <main className="contentShell">
+        <main className="contentShell" data-page={props.activePage}>
           {props.state === 'error' && <Badge variant="destructive">数据加载失败</Badge>}
           {props.children}
         </main>