refactor(frontend): P0 API 层收口与 http 统一

- 统一 http.ts baseURL：get/post/download/upload 均走 resolveApiUrl
- agentUtils 下沉至 lib/agent-utils，API 层移除对 components 的依赖
- 扩展 metricsApi/snmpApi/prometheusProxyApi/zabbixProxyApi
- 扩展 pipelineApi/credentialApi 覆盖流水线与凭证场景
- 14 个组件/页面禁止直连 http，统一走 @/services/api

frontend/src/components/server/ServerForm.tsx

@@ -25,7 +25,7 @@ import {
   SelectValue,
 } from '@/components/ui/select';
 import { Server, ChevronDown, Loader2, Save, Key, Shield } from 'lucide-react';
-import http from '@/services/http';
+import { credentialApi } from '@/services/api';
 
 // 表单数据结构
 export interface ServerFormData {
@@ -101,9 +101,9 @@ export function ServerForm({
   // 加载凭证列表
   useEffect(() => {
     if (open) {
-      http.get('/credentials')
+      credentialApi.list()
         .then(( res: any) => {
-          const list = Array.isArray(res) ? res : (res?.data || []);
+          const list = Array.isArray(res) ? res : (res?.list || res?.data || []);
           setCredentials(list);
         })
         .catch(() => setCredentials([]));