fix: 完善Agent系统信息上报

- 持续上报系统元数据并动态更新运行时长
- 兼容旧版心跳补齐资产运行时长
- 修复监控指标当前值重复显示单位

backend/controller/agent.go

@@ -150,6 +150,10 @@ func (h *AgentHandler) ReceiveReport(c *gin.Context) {
 			updates["uptime"] = req.System.Uptime
 		}
 	}
+	// 兼容旧版 Agent：系统信息缺席时使用心跳中的运行时长补齐资产元数据。 // Logan.Li
+	if _, ok := updates["uptime"]; !ok && req.Heartbeat.UptimeSec > 0 {
+		updates["uptime"] = req.Heartbeat.UptimeSec
+	}
 	var result *gorm.DB
 	if assetMatched {
 		result = h.db.Model(&model.Server{}).Where("id = ?", matchedServer.ID).Updates(updates)
@@ -162,19 +166,32 @@ func (h *AgentHandler) ReceiveReport(c *gin.Context) {
 	// 避免 Agent 每次上报（10s）都新建记录导致资产越来越多。
 	if result.Error == nil && result.RowsAffected == 0 {
 		osName := ""
+		kernel := ""
+		uptime := req.Heartbeat.UptimeSec
 		if req.System != nil {
 			osName = req.System.OSVersion
+			kernel = req.System.Kernel
+			if req.System.Uptime > 0 {
+				uptime = req.System.Uptime
+			}
 		}
 		var existing model.Server
 		if h.db.Where("hostname = ?", req.Hostname).Take(&existing).Error == nil {
 			// 已自动注册过 → 仅更新实时指标，不重复创建
-			h.db.Model(&existing).Updates(map[string]interface{}{
+			existingUpdates := map[string]interface{}{
 				"ip": matchIP, "os": osName, "cpu": req.CPU.CoreCount,
 				"memory": memMB, "disk": diskGB, "status": "running",
 				"agent_status": "online", "agent_version": req.AgentVersion,
 				"cpu_usage": req.CPU.UsagePercent, "memory_usage": req.Memory.UsagePercent,
 				"disk_usage": diskAvg,
-			})
+			}
+			if kernel != "" {
+				existingUpdates["kernel"] = kernel
+			}
+			if uptime > 0 {
+				existingUpdates["uptime"] = uptime
+			}
+			h.db.Model(&existing).Updates(existingUpdates)
 		} else {
 			// 真正的新主机 → 注册，hostname 无唯一索引时不使用 OnConflict。 // Logan.Li
 			newServer := model.Server{
@@ -190,6 +207,8 @@ func (h *AgentHandler) ReceiveReport(c *gin.Context) {
 				Status:       "running",
 				AgentStatus:  "online",
 				AgentVersion: req.AgentVersion,
+				Kernel:       kernel,
+				Uptime:       uptime,
 				CPUUsage:     req.CPU.UsagePercent,
 				MemoryUsage:  req.Memory.UsagePercent,
 				DiskUsage:    diskAvg,