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

agent/collector/network.go

@@ -0,0 +1,171 @@
+// Package collector 提供服务器各项系统指标的采集能力。
+// 本文件实现网络连接数、网卡流量等网络指标采集。
+//
+// 署名 Hermes (extended from Logan.Li pattern)
+package collector
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	"ezops/agent/model"
+)
+
+// netSample 保存上一次的网络采样数据，用于计算速率
+type netSample struct {
+	time     time.Time
+	rxBytes  uint64
+	txBytes  uint64
+}
+
+// NetworkCollector 网络指标采集器
+type NetworkCollector struct {
+	mu   sync.Mutex
+	prev *netSample
+}
+
+// NewNetworkCollector 创建网络采集器
+func NewNetworkCollector() *NetworkCollector {
+	return &NetworkCollector{}
+}
+
+// Collect 采集网络指标（并发连接数、TIME_WAIT、网卡 rx/tx B/s）
+func (c *NetworkCollector) Collect() (model.NetworkStat, error) {
+	stat := model.NetworkStat{}
+
+	// 1. 采集 TCP 连接统计
+	if tcpStat, err := readSockStat(); err == nil {
+		stat.TCPEstablished = tcpStat.established
+		stat.TCPTimeWait = tcpStat.timeWait
+		stat.TCPTotal = tcpStat.total
+	}
+
+	// 2. 采集网卡流量（取所有非 lo 网卡合计）
+	curRx, curTx, nicName, err := readNetDevTotal()
+	if err != nil {
+		return stat, fmt.Errorf("读取网卡流量失败: %w", err)
+	}
+	stat.NicName = nicName
+
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	now := time.Now()
+	cur := &netSample{time: now, rxBytes: curRx, txBytes: curTx}
+
+	if c.prev != nil && now.After(c.prev.time) {
+		elapsed := now.Sub(c.prev.time).Seconds()
+		if elapsed > 0 && cur.rxBytes >= c.prev.rxBytes && cur.txBytes >= c.prev.txBytes {
+			stat.NetRxBPS = float64(cur.rxBytes-c.prev.rxBytes) / elapsed
+			stat.NetTxBPS = float64(cur.txBytes-c.prev.txBytes) / elapsed
+		}
+	}
+	c.prev = cur
+
+	return stat, nil
+}
+
+// tcpSockStat 解析 /proc/net/sockstat 或 /proc/net/tcp 的结果
+type tcpSockStat struct {
+	established int
+	timeWait    int
+	total       int
+}
+
+// readSockStat 从 /proc/net/sockstat 读取 TCP 连接统计
+func readSockStat() (tcpSockStat, error) {
+	var result tcpSockStat
+
+	f, err := os.Open("/proc/net/sockstat")
+	if err != nil {
+		// Fallback: try /proc/net/sockstat6
+		return result, err
+	}
+	defer f.Close()
+
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		line := scanner.Text()
+		if !strings.HasPrefix(line, "TCP:") {
+			continue
+		}
+		// 格式: "TCP: inuse 123 orphan 0 tw 45 alloc 200 mem 30"
+		fields := strings.Fields(line)
+		for i, f := range fields {
+			switch f {
+			case "inuse":
+				if i+1 < len(fields) {
+					result.established, _ = strconv.Atoi(fields[i+1])
+				}
+			case "tw":
+				if i+1 < len(fields) {
+					result.timeWait, _ = strconv.Atoi(fields[i+1])
+				}
+			case "alloc":
+				if i+1 < len(fields) {
+					result.total, _ = strconv.Atoi(fields[i+1])
+				}
+			}
+		}
+		result.total = result.established // total = established count (inuse)
+		break
+	}
+
+	return result, scanner.Err()
+}
+
+// readNetDevTotal 读取 /proc/net/dev，取第一个非 lo 且活跃的物理网卡总流量
+func readNetDevTotal() (rxBytes, txBytes uint64, nicName string, err error) {
+	f, err := os.Open("/proc/net/dev")
+	if err != nil {
+		return 0, 0, "", err
+	}
+	defer f.Close()
+
+	scanner := bufio.NewScanner(f)
+	// Skip header lines (first 2 lines)
+	lineNum := 0
+	for scanner.Scan() {
+		lineNum++
+		if lineNum <= 2 {
+			continue
+		}
+		line := strings.TrimSpace(scanner.Text())
+		parts := strings.SplitN(line, ":", 2)
+		if len(parts) != 2 {
+			continue
+		}
+		name := strings.TrimSpace(parts[0])
+		// Skip loopback and virtual interfaces
+		if name == "lo" || strings.HasPrefix(name, "veth") || strings.HasPrefix(name, "docker") ||
+			strings.HasPrefix(name, "br-") || strings.HasPrefix(name, "virbr") {
+			continue
+		}
+
+		fields := strings.Fields(parts[1])
+		if len(fields) < 10 {
+			continue
+		}
+
+		// fields[0]=rx_bytes, fields[8]=tx_bytes
+		rb, _ := strconv.ParseUint(fields[0], 10, 64)
+		tb, _ := strconv.ParseUint(fields[8], 10, 64)
+
+		if rb > 0 || tb > 0 {
+			nicName = name
+			rxBytes += rb
+			txBytes += tb
+		}
+	}
+
+	if nicName == "" {
+		return 0, 0, "eth0", nil
+	}
+
+	return rxBytes, txBytes, nicName, scanner.Err()
+}