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/api/dashboard.ts

@@ -1,4 +1,5 @@
 import apiClient from './client'
+import { cachedRequest, buildCacheKey } from '@/utils/cache'
 
 export interface DashboardStat {
   name: string
@@ -289,8 +290,15 @@ export interface TimeRangeParams {
 export const dashboardApi = {
   // 获取仪表盘统计数据
   async getStats(params?: TimeRangeParams): Promise<DashboardStatsResponse> {
-    const response = await apiClient.get<DashboardStatsResponse>('/api/dashboard/stats', { params })
-    return response.data
+    const cacheKey = buildCacheKey('dashboard:stats', params)
+    return cachedRequest(
+      cacheKey,
+      async () => {
+        const response = await apiClient.get<DashboardStatsResponse>('/api/dashboard/stats', { params })
+        return response.data
+      },
+      10 * 1000
+    )
   },
 
   // 获取最近的请求记录
@@ -303,8 +311,14 @@ export const dashboardApi = {
 
   // 获取提供商状态
   async getProviderStatus(): Promise<ProviderStatus[]> {
-    const response = await apiClient.get<ProviderStatusResponse>('/api/dashboard/provider-status')
-    return response.data.providers
+    return cachedRequest(
+      'dashboard:provider-status',
+      async () => {
+        const response = await apiClient.get<ProviderStatusResponse>('/api/dashboard/provider-status')
+        return response.data.providers
+      },
+      20 * 1000
+    )
   },
 
   // 获取请求详情
@@ -316,10 +330,17 @@ export const dashboardApi = {
 
   // 获取每日统计数据
   async getDailyStats(params?: TimeRangeParams & { days?: number }): Promise<DailyStatsResponse> {
-    const response = await apiClient.get<DailyStatsResponse>('/api/dashboard/daily-stats', {
-      params
-    })
-    return response.data
+    const cacheKey = buildCacheKey('dashboard:daily-stats', params)
+    return cachedRequest(
+      cacheKey,
+      async () => {
+        const response = await apiClient.get<DailyStatsResponse>('/api/dashboard/daily-stats', {
+          params
+        })
+        return response.data
+      },
+      20 * 1000
+    )
   },
 
   // 获取 cURL 命令数据（含明文 API Key）