refactor(frontend): services/api 迁至 src/api，http 迁至 utils/request

对齐 Vue 后台惯例：
- src/api/          域 API（原 services/api）
- src/utils/request.ts  HTTP 封装（原 services/http.ts）
- src/utils/export.ts  客户端导出工具
- src/utils/index.ts   工具统一出口

全局导入改为 @/api 与 @/utils/request，tsc + build 通过。

frontend/src/components/dashboard/Dashboard.tsx

@@ -3,7 +3,7 @@ import { useNavigate } from 'react-router-dom';
 import { Button } from '@/components/ui/button';
 import { cn } from '@/lib/utils';
 import { Clock, Server, ArrowRight } from 'lucide-react';
-import { dashboardStatsApi, serverApi, kubernetesApi } from '@/services/api';
+import { dashboardStatsApi, serverApi, kubernetesApi } from '@/api';
 import { StatStrip } from '@/components/ui/stat-strip';
 import { CostOverviewCard, TopResourceUsageCard, ResourceUsageCard } from './DashboardCharts';
 import {