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/PerformanceAnalysis.vue

@@ -91,7 +91,7 @@
 </template>
 
 <script setup lang="ts">
-import { ref, computed, onMounted, watch } from 'vue'
+import { ref, computed, onMounted, onUnmounted, watch } from 'vue'
 import Card from '@/components/ui/card.vue'
 import { LoadingState, TimeRangePicker } from '@/components/common'
 import { ErrorDistributionChart, PercentileChart } from '@/components/stats'
@@ -112,6 +112,12 @@ const errorLoading = ref(false)
 
 const providerStatus = ref<ProviderStatus[]>([])
 const providerLoading = ref(false)
+let percentilesRequestId = 0
+let errorsRequestId = 0
+let providersRequestId = 0
+let loadAllPromise: Promise<void> | null = null
+let hasPendingLoadAll = false
+let loadAllDebounceTimer: ReturnType<typeof setTimeout> | null = null
 
 function buildTimeRangeParams() {
   return {
@@ -124,31 +130,45 @@ function buildTimeRangeParams() {
 }
 
 async function loadPercentiles() {
+  const requestId = ++percentilesRequestId
   percentileLoading.value = true
   try {
-    percentiles.value = await adminApi.getPercentiles(buildTimeRangeParams())
+    const data = await adminApi.getPercentiles(buildTimeRangeParams())
+    if (requestId !== percentilesRequestId) return
+    percentiles.value = data
   } finally {
-    percentileLoading.value = false
+    if (requestId === percentilesRequestId) {
+      percentileLoading.value = false
+    }
   }
 }
 
 async function loadErrors() {
+  const requestId = ++errorsRequestId
   errorLoading.value = true
   try {
     const response = await adminApi.getErrorDistribution(buildTimeRangeParams())
+    if (requestId !== errorsRequestId) return
     errorDistribution.value = response.distribution
     errorTrend.value = response.trend
   } finally {
-    errorLoading.value = false
+    if (requestId === errorsRequestId) {
+      errorLoading.value = false
+    }
   }
 }
 
 async function loadProviders() {
+  const requestId = ++providersRequestId
   providerLoading.value = true
   try {
-    providerStatus.value = await dashboardApi.getProviderStatus()
+    const data = await dashboardApi.getProviderStatus()
+    if (requestId !== providersRequestId) return
+    providerStatus.value = data
   } finally {
-    providerLoading.value = false
+    if (requestId === providersRequestId) {
+      providerLoading.value = false
+    }
   }
 }
 
@@ -166,10 +186,47 @@ const errorTrendChartData = computed(() => ({
 }))
 
 async function loadAll() {
-  await Promise.all([loadPercentiles(), loadErrors(), loadProviders()])
+  if (loadAllPromise) {
+    hasPendingLoadAll = true
+    return loadAllPromise
+  }
+  loadAllPromise = Promise.all([loadPercentiles(), loadErrors(), loadProviders()])
+    .then(() => undefined)
+    .finally(() => {
+      loadAllPromise = null
+      if (hasPendingLoadAll) {
+        hasPendingLoadAll = false
+        void loadAll()
+      }
+    })
+  return loadAllPromise
 }
 
-watch(timeRange, loadAll, { deep: true })
+function scheduleLoadAll() {
+  if (loadAllDebounceTimer) {
+    clearTimeout(loadAllDebounceTimer)
+  }
+  loadAllDebounceTimer = setTimeout(() => {
+    loadAllDebounceTimer = null
+    void loadAll()
+  }, 120)
+}
 
-onMounted(loadAll)
+watch(timeRange, scheduleLoadAll, { deep: true })
+
+onMounted(() => {
+  void loadAll()
+})
+
+onUnmounted(() => {
+  if (loadAllDebounceTimer) {
+    clearTimeout(loadAllDebounceTimer)
+    loadAllDebounceTimer = null
+  }
+  hasPendingLoadAll = false
+  loadAllPromise = null
+  percentilesRequestId += 1
+  errorsRequestId += 1
+  providersRequestId += 1
+})
 </script>