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/handlers/site.go

@@ -0,0 +1,166 @@
+package handlers
+
+import (
+	"ezops/internal/models"
+	"net/http"
+	"strconv"
+
+	"github.com/gin-gonic/gin"
+	"gorm.io/gorm"
+)
+
+// SiteHandler 站点拨测管理 handler // Logan.Li
+type SiteHandler struct {
+	db *gorm.DB
+}
+
+// NewSiteHandler 创建站点拨测 handler
+func NewSiteHandler(db *gorm.DB) *SiteHandler {
+	return &SiteHandler{db: db}
+}
+
+// ========== Site Task CRUD ==========
+
+// ListTasks 列出拨测任务
+// GET /api/v1/site/tasks?page=1&page_size=20&type=&status=
+func (h *SiteHandler) ListTasks(c *gin.Context) {
+	var tasks []models.SiteTask
+	q := h.db.Model(&models.SiteTask{})
+
+	if t := c.Query("type"); t != "" {
+		q = q.Where("type = ?", t)
+	}
+	if s := c.Query("status"); s != "" {
+		q = q.Where("status = ?", s)
+	}
+	if kw := c.Query("keyword"); kw != "" {
+		q = q.Where("name LIKE ? OR url LIKE ?", "%"+kw+"%", "%"+kw+"%")
+	}
+
+	page, _ := strconv.Atoi(c.DefaultQuery("page", "1"))
+	pageSize, _ := strconv.Atoi(c.DefaultQuery("page_size", "20"))
+	var total int64
+	q.Count(&total)
+	q.Offset((page - 1) * pageSize).Limit(pageSize).Order("name ASC").Find(&tasks)
+
+	if tasks == nil {
+		tasks = []models.SiteTask{}
+	}
+	c.JSON(http.StatusOK, models.Response{Code: 200, Data: gin.H{"list": tasks, "total": total}})
+}
+
+// CreateTask 创建拨测任务
+// POST /api/v1/site/tasks
+func (h *SiteHandler) CreateTask(c *gin.Context) {
+	var task models.SiteTask
+	if err := c.ShouldBindJSON(&task); err != nil {
+		c.JSON(http.StatusBadRequest, models.Response{Code: 400, Message: err.Error()})
+		return
+	}
+	if err := h.db.Create(&task).Error; err != nil {
+		c.JSON(http.StatusInternalServerError, models.Response{Code: 500, Message: err.Error()})
+		return
+	}
+	c.JSON(http.StatusOK, models.Response{Code: 200, Data: task, Message: "创建成功"})
+}
+
+// UpdateTask 更新拨测任务
+// PUT /api/v1/site/tasks/:id
+func (h *SiteHandler) UpdateTask(c *gin.Context) {
+	id := c.Param("id")
+	var task models.SiteTask
+	if err := h.db.First(&task, id).Error; err != nil {
+		c.JSON(http.StatusNotFound, models.Response{Code: 404, Message: "任务不存在"})
+		return
+	}
+	if err := c.ShouldBindJSON(&task); err != nil {
+		c.JSON(http.StatusBadRequest, models.Response{Code: 400, Message: err.Error()})
+		return
+	}
+	h.db.Save(&task)
+	c.JSON(http.StatusOK, models.Response{Code: 200, Data: task, Message: "更新成功"})
+}
+
+// DeleteTask 删除拨测任务
+// DELETE /api/v1/site/tasks/:id
+func (h *SiteHandler) DeleteTask(c *gin.Context) {
+	id := c.Param("id")
+	if err := h.db.Delete(&models.SiteTask{}, id).Error; err != nil {
+		c.JSON(http.StatusInternalServerError, models.Response{Code: 500, Message: err.Error()})
+		return
+	}
+	c.JSON(http.StatusOK, models.Response{Code: 200, Message: "删除成功"})
+}
+
+// BatchDeleteTasks 批量删除
+// DELETE /api/v1/site/tasks/batch-delete
+func (h *SiteHandler) BatchDeleteTasks(c *gin.Context) {
+	var req models.IDsRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, models.Response{Code: 400, Message: err.Error()})
+		return
+	}
+	h.db.Where("id IN ?", req.IDs).Delete(&models.SiteTask{})
+	c.JSON(http.StatusOK, models.Response{Code: 200, Message: "批量删除成功"})
+}
+
+// ========== Site Results ==========
+
+// ListResults 查询拨测结果
+// GET /api/v1/site/results?task_id=N&from=&to=&limit=100
+func (h *SiteHandler) ListResults(c *gin.Context) {
+	var results []models.SiteResult
+	q := h.db.Model(&models.SiteResult{})
+
+	if tid := c.Query("task_id"); tid != "" {
+		q = q.Where("task_id = ?", tid)
+	}
+	if from := c.Query("from"); from != "" {
+		q = q.Where("created_at >= ?", from)
+	}
+	if to := c.Query("to"); to != "" {
+		q = q.Where("created_at <= ?", to)
+	}
+
+	limit, _ := strconv.Atoi(c.DefaultQuery("limit", "100"))
+	q.Order("created_at DESC").Limit(limit).Find(&results)
+
+	if results == nil {
+		results = []models.SiteResult{}
+	}
+	c.JSON(http.StatusOK, models.Response{Code: 200, Data: results})
+}
+
+// ========== Site Statistics ==========
+
+// GetSiteStats 获取拨测概览统计
+// GET /api/v1/site/stats
+func (h *SiteHandler) GetSiteStats(c *gin.Context) {
+	var total, normal, abnormal int64
+	h.db.Model(&models.SiteTask{}).Count(&total)
+	h.db.Model(&models.SiteTask{}).Where("status = ?", "active").Count(&normal)
+	h.db.Model(&models.SiteTask{}).Where("status = ?", "error").Count(&abnormal)
+
+	// Calculate availability rate from recent results
+	var availRate float64
+	if total > 0 {
+		var successCount int64
+		h.db.Model(&models.SiteResult{}).
+			Where("created_at > datetime('now', '-1 hour') AND status = 'success'").
+			Count(&successCount)
+		var totalRecent int64
+		h.db.Model(&models.SiteResult{}).
+			Where("created_at > datetime('now', '-1 hour')").
+			Count(&totalRecent)
+		if totalRecent > 0 {
+			availRate = float64(successCount) / float64(totalRecent) * 100
+		}
+	}
+
+	c.JSON(http.StatusOK, models.Response{Code: 200, Data: gin.H{
+		"total":       total,
+		"normal":      normal,
+		"abnormal":    abnormal,
+		"avail_rate":  availRate,
+	}})
+}