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/agent/AgentAlerts.tsx

@@ -2,7 +2,7 @@
 import { useState, useEffect, useCallback } from 'react';
 import { toast } from 'sonner';
 import { useConfirm } from '@/components/ui/confirm-dialog';
-import { agentApi } from '@/services/api';
+import { agentApi } from '@/api';
 import { Card, CardContent } from '@/components/ui/card';
 import { Button } from '@/components/ui/button';
 import { Badge } from '@/components/ui/badge';

frontend/src/components/agent/AgentMonitor.tsx

@@ -1,6 +1,6 @@
 import { useState, useEffect, useRef, useCallback } from 'react';
 import { toast } from 'sonner';
-import { agentApi } from '@/services/api';
+import { agentApi } from '@/api';
 import { AgentWizard } from './AgentWizard';
 import { HostDetailDialog } from './HostDetailDialog';
 import { isOnline, timeAgo, asList } from './agentUtils';

frontend/src/components/agent/AgentRuleDialog.tsx

@@ -1,7 +1,7 @@
 // Agent 告警规则编辑/新建弹窗（自包含表单状态，从 AgentAlerts.tsx 提取） // Logan.Li
 import { useState, useEffect } from 'react';
 import { toast } from 'sonner';
-import { agentApi } from '@/services/api';
+import { agentApi } from '@/api';
 import { Button } from '@/components/ui/button';
 import { Input } from '@/components/ui/input';
 import { Label } from '@/components/ui/label';

frontend/src/components/agent/AgentWizard.tsx

@@ -12,7 +12,7 @@ import { Button } from '@/components/ui/button';
 import { Input } from '@/components/ui/input';
 import { Label } from '@/components/ui/label';
 import { Copy, Check, Terminal, Download, Settings, Play, Cpu, Zap, Loader2, Server, Shield } from 'lucide-react';
-import { serverApi } from '@/services/api';
+import { serverApi } from '@/api';
 import { toast } from 'sonner';
 
 interface AgentWizardProps {

frontend/src/components/agent/HostDetailDialog.tsx

@@ -1,6 +1,6 @@
 // 主机详情弹窗：展示历史指标趋势图 + 端口发现列表（从 AgentMonitor.tsx 提取） // Logan.Li
 import { useState, useEffect } from 'react';
-import { agentApi } from '@/services/api';
+import { agentApi } from '@/api';
 import { isOnline, timeAgo, asList } from './agentUtils';
 import { Button } from '@/components/ui/button';
 import { Badge } from '@/components/ui/badge';