feat: Redis热数据+K线聚合+Dashboard MySQL指标修复

backend/internal/api/handlers/dashboard.go

@@ -294,17 +294,17 @@ func (h *DashboardHandler) GetMetrics(c *gin.Context) {
 		}
 	}
 
-	// 从 agent_reports 表查最近 N 小时的真实数据 // Logan.Li
+	// 从 agent_reports 表查最近 N 小时的真实数据（MySQL 聚合）
 	since := time.Now().Add(-time.Duration(hours) * time.Hour)
 	type avgPoint struct {
-		Bucket string  // strftime 返回字符串 "2006-01-02 15:00"，不能直接扫入 time.Time（会得零值）
+		Bucket string
 		AvgCPU float64
 		AvgMem float64
 	}
 	var rows []avgPoint
 	h.db.Model(&models.AgentReport{}).
-		Select("strftime('%Y-%m-%d %H:00', created_at) as bucket, AVG(cpu_usage) as avg_cpu, AVG(mem_usage) as avg_mem").
-		Where("created_at >= ?", since).
+		Select("DATE_FORMAT(report_time, '%Y-%m-%d %H:00') as bucket, ROUND(AVG(cpu_usage),2) as avg_cpu, ROUND(AVG(mem_usage),2) as avg_mem").
+		Where("report_time >= ?", since).
 		Group("bucket").
 		Order("bucket ASC").
 		Scan(&rows)