feat: 重构监控中心导航，新增资源监控4大模块

- 主菜单「监控告警」→「监控中心」
- 「告警中心」→「告警服务」移至链路追踪下方
- 新增资源监控 Tab 页（主机/中间件/SNMP/站点拨测）
- Agent 新增网络采集器(network)和磁盘IO采集器(diskio)
- 后端扩展 Agent 上报模型，支持 NetworkStat/DiskIOStat
- 前端 ServerTableRow 展示网络和磁盘IO实时指标
- WebSocket MetricsUpdate 推送扩展

frontend/src/components/server/ServerManager.tsx

@@ -1,4 +1,4 @@
-import { useState, useEffect } from 'react';
+import { useState, useEffect, useRef } from 'react';
 import { cn } from '@/lib/utils';
 import { Card, CardContent } from '@/components/ui/card';
 import { Button } from '@/components/ui/button';
@@ -168,6 +168,82 @@ export function ServerManager() {
     loadData();
   }, []);
 
+  // WebSocket 实时接收 Agent 指标推送 // Logan.Li
+  const wsRef = useRef<WebSocket | null>(null);
+  const reconnectTimerRef = useRef<ReturnType<typeof setTimeout> | null>(null);
+
+  useEffect(() => {
+    const token = useUserStore.getState().token;
+    if (!token) return;
+
+    const protocol = window.location.protocol === 'https:' ? 'wss:' : 'ws:';
+    const wsUrl = `${protocol}//${window.location.host}/ws/metrics?token=${token}`;
+
+    const connect = () => {
+      if (wsRef.current?.readyState === WebSocket.OPEN) return;
+
+      const ws = new WebSocket(wsUrl);
+      wsRef.current = ws;
+
+      ws.onopen = () => {
+        console.log('[MetricsWS] 已连接，实时接收指标推送');
+      };
+
+      ws.onmessage = (event) => {
+        try {
+          const msg = JSON.parse(event.data);
+          if (msg.type === 'metrics_update') {
+            setServers((prev) =>
+              prev.map((s) => {
+                // 通过 hostname 匹配（Agent 上报时使用 hostname）
+                if (s.hostname === msg.hostname) {
+                  return {
+                    ...s,
+                    cpu_usage: msg.cpu_usage,
+                    memory_usage: msg.memory_usage,
+                    disk_usage: msg.disk_usage,
+                    status: msg.status,
+                    tcp_established: msg.tcp_established,
+                    tcp_time_wait: msg.tcp_time_wait,
+                    net_rx_bps: msg.net_rx_bps,
+                    net_tx_bps: msg.net_tx_bps,
+                    disk_read_bps: msg.disk_read_bps,
+                    disk_write_bps: msg.disk_write_bps,
+                  };
+                }
+                return s;
+              })
+            );
+          }
+        } catch (e) {
+          // 忽略非 JSON 消息
+        }
+      };
+
+      ws.onclose = () => {
+        console.log('[MetricsWS] 连接断开，3 秒后重连');
+        wsRef.current = null;
+        reconnectTimerRef.current = setTimeout(connect, 3000);
+      };
+
+      ws.onerror = (err) => {
+        console.error('[MetricsWS] 连接错误:', err);
+        ws.close();
+      };
+    };
+
+    connect();
+
+    return () => {
+      if (reconnectTimerRef.current) clearTimeout(reconnectTimerRef.current);
+      if (wsRef.current) {
+        wsRef.current.onclose = null; // 阻止自动重连
+        wsRef.current.close();
+        wsRef.current = null;
+      }
+    };
+  }, []);
+
   const filteredServers = servers.filter((server) => {
     const matchesSearch =
       (server.hostname || '').toLowerCase().includes(searchQuery.toLowerCase()) ||