refactor(mp): request.ts 模块级状态收编 + AbortSignal + Analytics 受控

- 提取 ConcurrencyLimiter 类（并发限制 8，可 reset）
- 提取 ResponseCache 类（GET 缓存 + 去重 + patientId 绑定）
- 新增 resetForTesting() 测试隔离函数
- api.get/post/put/delete 支持 AbortSignal 请求取消
- app.tsx Analytics 定时器改为 useDidShow/useDidHide 控制后台暂停
- 测试文件接入 resetForTesting()

构建通过，测试 74/75（1 个预存失败）。

apps/miniprogram/src/app.tsx

@@ -1,5 +1,5 @@
-import { useEffect, PropsWithChildren } from 'react';
-import Taro, { useDidShow } from '@tarojs/taro';
+import { useEffect, useRef, PropsWithChildren } from 'react';
+import Taro, { useDidShow, useDidHide } from '@tarojs/taro';
 import ErrorBoundary from './components/ErrorBoundary';
 import { flushEvents } from './services/analytics';
 import { useAuthStore } from './stores/auth';
@@ -28,16 +28,32 @@ function App({ children }: PropsWithChildren<Record<string, unknown>>) {
     return () => { delete (globalThis as any).__hms; };
   }, []);
 
+  // Analytics 定时器：仅在页面可见时运行，后台时暂停以节省资源
+  const analyticsTimerRef = useRef<ReturnType<typeof setInterval> | null>(null);
+
+  const startAnalyticsTimer = () => {
+    if (analyticsTimerRef.current) return;
+    analyticsTimerRef.current = setInterval(flushEvents, 30000);
+  };
+
+  const stopAnalyticsTimer = () => {
+    if (analyticsTimerRef.current) {
+      clearInterval(analyticsTimerRef.current);
+      analyticsTimerRef.current = null;
+    }
+  };
+
+  useDidShow(() => {
+    startAnalyticsTimer();
+  });
+
+  useDidHide(() => {
+    stopAnalyticsTimer();
+    flushEvents();
+  });
+
   useEffect(() => {
-    const timer = setInterval(() => {
-      flushEvents();
-    }, 30000);
-    const onHide = () => { flushEvents(); };
-    Taro.eventCenter.on('appHide', onHide);
-    return () => {
-      clearInterval(timer);
-      Taro.eventCenter.off('appHide', onHide);
-    };
+    return () => { stopAnalyticsTimer(); };
   }, []);
 
   return <ErrorBoundary>{children}</ErrorBoundary>;