feat: 监控告警体系统一重构 + 自动化任务调度引擎 + 监控大屏拆分

告警中心
- 新增统一告警(alert_unified)、监控告警规则(monitor_alert_rule)、指标目录(alert_metric_catalog)
- 通知策略与消息分发(alert_notify_policy/dispatch/message)、静默规则
- 告警引擎按阈值/SNMP 拆分(alert_engine_monitor/snmp)

监控采集
- SNMP 常量/模板与历史指标(snmp templates/constants、snmp_metrics_history、snmp_collect)
- 中间件监控 Redis 采集与种子(middleware_monitor_redis/seed)
- 站点探测 pkg(siteprobe) + 站点视图(site_view)

自动化任务
- cron 调度器(cronscheduler)、脚本运行器(scriptrunner)、系统任务(systask)及运行记录(cron_job_run、system_task)

审计与凭证
- 审计设置(audit_setting) + 历史清理(auditcleaner)

前端
- 监控页面(host/middleware/site/snmp)拆分为子模块并大屏化
- 告警中心多 Tab(规则/指标目录/通知策略/静默)、任务管理组件重构、Agent CLI Markdown 渲染
- 移除旧脚本卡片/详情/日志组件，统一为 ScriptTable/ScriptCodeEditor/TerminalOutput

Co-Authored-By: Claude <noreply@anthropic.com>

backend/controller/agent.go

@@ -335,18 +335,82 @@ func (h *AgentHandler) GetLatestReports(c *gin.Context) {
 	})
 }
 
+// parseFlexibleTime 解析前端传入的时间（ISO / datetime-local） // Logan.Li
+func parseFlexibleTime(s string) (time.Time, error) {
+	s = strings.TrimSpace(s)
+	layouts := []string{
+		time.RFC3339,
+		"2006-01-02T15:04:05Z07:00",
+		"2006-01-02 15:04:05",
+		"2006-01-02T15:04",
+		"2006-01-02 15:04",
+	}
+	for _, layout := range layouts {
+		if t, err := time.ParseInLocation(layout, s, time.Local); err == nil {
+			return t, nil
+		}
+	}
+	return time.Time{}, fmt.Errorf("无法解析时间: %s", s)
+}
+
+// resolveHostHistoryRange 解析历史查询时间范围（minutes / hours / start+end） // Logan.Li
+func resolveHostHistoryRange(c *gin.Context) (since, until time.Time, err error) {
+	until = time.Now()
+	if startStr := strings.TrimSpace(c.Query("start")); startStr != "" {
+		endStr := strings.TrimSpace(c.Query("end"))
+		if endStr == "" {
+			return since, until, fmt.Errorf("自定义范围缺少 end 参数")
+		}
+		since, err = parseFlexibleTime(startStr)
+		if err != nil {
+			return since, until, err
+		}
+		until, err = parseFlexibleTime(endStr)
+		if err != nil {
+			return since, until, err
+		}
+		if until.Before(since) {
+			since, until = until, since
+		}
+		return since, until, nil
+	}
+	if minStr := strings.TrimSpace(c.Query("minutes")); minStr != "" {
+		mins, _ := strconv.Atoi(minStr)
+		if mins <= 0 {
+			mins = 60
+		}
+		if mins > 43200 {
+			mins = 43200
+		}
+		since = until.Add(-time.Duration(mins) * time.Minute)
+		return since, until, nil
+	}
+	hours := 1
+	if v := strings.TrimSpace(c.Query("hours")); v != "" {
+		hours, _ = strconv.Atoi(v)
+		if hours <= 0 {
+			hours = 1
+		}
+		if hours > 720 {
+			hours = 720
+		}
+	}
+	since = until.Add(-time.Duration(hours) * time.Hour)
+	return since, until, nil
+}
+
 // GetHostHistory 获取指定主机的历史指标
-// GET /api/v1/agent/history/:hostname?hours=1
+// GET /api/v1/agent/history/:hostname?minutes=60 | ?hours=1 | ?start=&end=
 func (h *AgentHandler) GetHostHistory(c *gin.Context) {
 	hostname := c.Param("hostname")
-	hours := 1
-	if v := c.Query("hours"); v != "" {
-		fmt.Sscanf(v, "%d", &hours)
+	since, until, err := resolveHostHistoryRange(c)
+	if err != nil {
+		c.JSON(http.StatusBadRequest, model.Response{Code: 400, Message: err.Error()})
+		return
 	}
-	since := time.Now().Add(-time.Duration(hours) * time.Hour)
 
 	var reports []model.AgentReport
-	h.db.Where("hostname = ? AND report_time >= ?", hostname, since).
+	h.db.Where("hostname = ? AND report_time >= ? AND report_time <= ?", hostname, since, until).
 		Order("report_time ASC").
 		Find(&reports)