fix(web): harden route transitions and monitor memory

vehicle-data-platform/apps/web/src/v2/shared/AsyncState.tsx

@@ -1,7 +1,10 @@
 import { IconAlertTriangle, IconRefresh } from '@douyinfe/semi-icons';
 
 export function PageLoading({ label = '正在加载车辆数据' }: { label?: string }) {
-  return <div className="v2-page-state"><span className="v2-spinner" />{label}</div>;
+  return <section className="v2-page-state" role="status" aria-live="polite">
+    <header><span className="v2-spinner" /><div><strong>{label}</strong><small>导航与筛选状态已保留</small></div></header>
+    <div className="v2-page-skeleton"><i /><i /><i /><i /></div>
+  </section>;
 }
 
 export function InlineError({ message, onRetry }: { message: string; onRetry?: () => void }) {