feat(mp): App 级告警长轮询 + 健康总览 TS 修复

- 新增 useAlertPolling hook：10s 间隔轮询 critical 告警
- requestUnlimited 独立通道，不占并发槽位
- generation counter 防重叠 + 失败指数退避(max 30s/10次)
- 新告警弹窗 Taro.showModal + TabBar 角标
- 修复 HealthThreshold 属性名(indicator/level 非 indicator_name/severity)
- 修复 usePageData fetchData 返回类型

apps/miniprogram/src/app.tsx

@@ -5,6 +5,7 @@ import ErrorBoundary from './components/ErrorBoundary';
 import { flushEvents } from './services/analytics';
 import { useAuthStore } from './stores/auth';
 import { useUIStore } from './stores/ui';
+import { useAlertPolling } from './hooks/useAlertPolling';
 import { migrateLegacyStorage } from './utils/secure-storage';
 import './app.scss';
 
@@ -19,6 +20,9 @@ function App({ children }: PropsWithChildren<Record<string, unknown>>) {
     restoreUI();
   });
 
+  // 告警轮询：登录态下自动监听 critical 告警
+  useAlertPolling();
+
   // 暴露全局 bridge 供 MCP/自动化测试调用（仅 dev 模式）
   useEffect(() => {
     if (process.env.NODE_ENV === 'production') return;