perf: 全栈查询优化、前端缓存去重与页面可见性优化

后端:
- SQL count 查询统一改用 func.count() 子查询替代 query.count()
- Dashboard/Audit 等页面多次独立查询合并为单次聚合查询
- Provider summary 列表改为批量查询消除 N+1 问题
- DailyStats 逐天循环查询改为 CASE 分桶单次查询
- 使用 load_only() 减少不必要的列加载
- cache_decorator 支持嵌套属性路径解析(dotted vary_by)
- 多个管理/公共端点新增 @cache_result 缓存装饰

前端:
- cache.ts 新增 in-flight 请求复用、dedupedRequest、buildCacheKey
- 大量 API 调用添加前端缓存或去重
- 多个页面定时器在标签页隐藏时暂停、可见时恢复
- Auth 检查从 setInterval 改为 storage + visibilitychange 事件驱动
- 请求竞态防护(requestId 模式)

数据库:
- Usage 表新增 idx_usage_status_user_created 复合索引

frontend/src/views/admin/AsyncTasks.vue

@@ -911,6 +911,8 @@ const showDetail = ref(false)
 const selectedTask = ref<AsyncTaskDetail | null>(null)
 const detailAutoRefresh = ref(false)
 let detailRefreshInterval: ReturnType<typeof setInterval> | null = null
+const isPageVisible = ref(typeof document === 'undefined' ? true : !document.hidden)
+let overviewRefreshInFlight = false
 
 // 使用记录详情抽屉状态
 const usageDetailOpen = ref(false)
@@ -953,6 +955,16 @@ async function fetchStats() {
   }
 }
 
+async function refreshOverview() {
+  if (overviewRefreshInFlight) return
+  overviewRefreshInFlight = true
+  try {
+    await Promise.all([fetchTasks(), fetchStats()])
+  } finally {
+    overviewRefreshInFlight = false
+  }
+}
+
 // 打开任务详情
 async function openTaskDetail(task: AsyncTaskItem) {
   try {
@@ -993,22 +1005,27 @@ function toggleDetailAutoRefresh() {
 
 // 开始详情自动刷新
 function startDetailAutoRefresh() {
+  if (!isPageVisible.value) return
   if (detailRefreshInterval) return
   // 立即刷新一次
   refreshTaskDetail()
   detailRefreshInterval = setInterval(() => {
-    if (selectedTask.value && showDetail.value) {
+    if (isPageVisible.value && selectedTask.value && showDetail.value) {
       refreshTaskDetail()
     }
   }, 5000)
 }
 
-// 停止详情自动刷新
-function stopDetailAutoRefresh() {
+function pauseDetailAutoRefresh() {
   if (detailRefreshInterval) {
     clearInterval(detailRefreshInterval)
     detailRefreshInterval = null
   }
+}
+
+// 停止详情自动刷新
+function stopDetailAutoRefresh() {
+  pauseDetailAutoRefresh()
   detailAutoRefresh.value = false
 }
 
@@ -1052,8 +1069,7 @@ async function cancelTask(task: AsyncTaskItem | AsyncTaskDetail) {
     toast({
       title: '任务已取消',
     })
-    fetchTasks()
-    fetchStats()
+    await refreshOverview()
     if (showDetail.value) {
       closeDetail()
     }
@@ -1222,11 +1238,11 @@ let autoRefreshInterval: ReturnType<typeof setInterval> | null = null
 const AUTO_REFRESH_INTERVAL = 5000 // 5秒
 
 function startAutoRefresh() {
+  if (!isPageVisible.value) return
   if (autoRefreshInterval) return
   autoRefreshInterval = setInterval(() => {
-    if (hasProcessingTasks.value && !loading.value) {
-      fetchTasks()
-      fetchStats()
+    if (isPageVisible.value && hasProcessingTasks.value && !loading.value) {
+      refreshOverview()
     }
   }, AUTO_REFRESH_INTERVAL)
 }
@@ -1240,19 +1256,35 @@ function stopAutoRefresh() {
 
 // 监听是否有进行中的任务，动态启停自动刷新
 watch(hasProcessingTasks, (has) => {
-  if (has) {
+  if (has && isPageVisible.value) {
     startAutoRefresh()
   } else {
     stopAutoRefresh()
   }
 }, { immediate: true })
 
+function handleVisibilityChange() {
+  isPageVisible.value = !document.hidden
+  if (!isPageVisible.value) {
+    stopAutoRefresh()
+    pauseDetailAutoRefresh()
+    return
+  }
+  if (hasProcessingTasks.value) {
+    startAutoRefresh()
+  }
+  if (detailAutoRefresh.value && selectedTask.value && showDetail.value) {
+    startDetailAutoRefresh()
+  }
+}
+
 onMounted(() => {
-  fetchTasks()
-  fetchStats()
+  document.addEventListener('visibilitychange', handleVisibilityChange)
+  refreshOverview()
 })
 
 onUnmounted(() => {
+  document.removeEventListener('visibilitychange', handleVisibilityChange)
   stopAutoRefresh()
   stopDetailAutoRefresh()
   clearTimeout(filterTimeout)