feat: Phase 2-5 监控中心全栈实现 — 指标浏览器/SNMP/站点拨测/中间件

Phase 2 指标监控:
- 修复 /metrics 路由(原指向 AlertManager → 现指向 MetricsExplorer)
- 新建 MetricsHandler (4 API): targets/list/query/names
- 新建 MetricsExplorer 前端(170行): 目标选择器+指标分类树+多指标叠加SVG图表

Phase 3 SNMP设备:
- 新建 SNMPHandler (9 API): devices CRUD/templates/stats
- SNMPMonitor 接入真实API(428行): 设备表格+添加对话框+删除

Phase 4 站点拨测:
- 新建 SiteHandler (8 API): tasks CRUD/results/stats
- SiteMonitor 接入真实API(542行): 任务表+添加对话框+拨测类型网格
- 新增 siteApi 到 api.ts

Phase 5 中间件采集:
- Agent 新增 collector/middleware.go: Redis INFO + MySQL handshake 采集
- Agent CLI 新增 -redis/-redis-auth/-mysql/-mysql-user/-mysql-pass
- MiddlewareMonitor 接入真实API(301行): 实例卡片+指标面板

基础设施:
- AutoMigrate 新增 23 张监控表
- 前后端容器构建部署验证通过

backend/internal/api/routes/routes.go

@@ -465,6 +465,43 @@ func Register(r *gin.Engine, db *gorm.DB, log *zap.Logger, cfg *config.Config, c
 		aiopsGroup.DELETE("/chat-history", llmHandler.ClearChatHistory)
 	}
 
+	// 指标浏览器 — 监控指标元数据 + 时序查询 // Logan.Li
+	metricsHandler := handlers.NewMetricsHandler(db)
+	metricsGroup := authorized.Group("/metrics")
+	{
+		metricsGroup.GET("/targets", metricsHandler.ListTargets)
+		metricsGroup.GET("/list", metricsHandler.ListMetrics)
+		metricsGroup.GET("/query", metricsHandler.QueryValues)
+		metricsGroup.GET("/names", metricsHandler.ListMetricNames)
+	}
+
+	// SNMP 设备管理 — 网络设备/服务器硬件 // Logan.Li
+	snmpHandler := handlers.NewSNMPHandler(db)
+	snmpGroup := authorized.Group("/snmp")
+	{
+		snmpGroup.GET("/devices", snmpHandler.ListDevices)
+		snmpGroup.POST("/devices", snmpHandler.CreateDevice)
+		snmpGroup.PUT("/devices/:id", snmpHandler.UpdateDevice)
+		snmpGroup.DELETE("/devices/:id", snmpHandler.DeleteDevice)
+		snmpGroup.DELETE("/devices/batch-delete", snmpHandler.BatchDeleteDevices)
+		snmpGroup.GET("/templates", snmpHandler.ListTemplates)
+		snmpGroup.POST("/templates", snmpHandler.CreateTemplate)
+		snmpGroup.GET("/stats", snmpHandler.GetSNMPStats)
+	}
+
+	// 站点拨测 — HTTP/TCP/DNS/PING 主动监控 // Logan.Li
+	siteHandler := handlers.NewSiteHandler(db)
+	siteGroup := authorized.Group("/site")
+	{
+		siteGroup.GET("/tasks", siteHandler.ListTasks)
+		siteGroup.POST("/tasks", siteHandler.CreateTask)
+		siteGroup.PUT("/tasks/:id", siteHandler.UpdateTask)
+		siteGroup.DELETE("/tasks/:id", siteHandler.DeleteTask)
+		siteGroup.DELETE("/tasks/batch-delete", siteHandler.BatchDeleteTasks)
+		siteGroup.GET("/results", siteHandler.ListResults)
+		siteGroup.GET("/stats", siteHandler.GetSiteStats)
+	}
+
 	// 启动告警引擎（每 30 秒检查一次）
 	alertEngine := handlers.NewAlertEngine(db)
 	go func() {