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_report_test.go

@@ -79,6 +79,51 @@ func TestReceiveReportMatchesExistingAssetByIP(t *testing.T) {
 	}
 }
 
+func TestReceiveReportUsesHeartbeatUptimeWithoutSystemPayload(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	db, err := gorm.Open(sqlite.Open("file:agent_report_heartbeat_uptime?mode=memory&cache=shared"), &gorm.Config{
+		Logger: gormlogger.Default.LogMode(gormlogger.Silent),
+	})
+	if err != nil {
+		t.Fatalf("打开测试数据库失败: %v", err)
+	}
+	if err := db.AutoMigrate(&model.Server{}, &model.AgentReport{}, &model.HealthProbe{}); err != nil {
+		t.Fatalf("迁移测试表失败: %v", err)
+	}
+
+	server := model.Server{Hostname: "c-monitor", IP: "172.19.16.113", Status: "running"}
+	if err := db.Create(&server).Error; err != nil {
+		t.Fatalf("创建测试资产失败: %v", err)
+	}
+
+	body := []byte(`{
+		"hostname":"c-monitor",
+		"ip":"172.19.16.113",
+		"agent_version":"v2.1.0",
+		"cpu":{"usage_percent":1.5,"core_count":4},
+		"memory":{"total_gb":15.1,"used_gb":1.8,"available_gb":13.3,"usage_percent":11.9},
+		"heartbeat":{"uptime_sec":7200}
+	}`)
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/agent/report", bytes.NewReader(body))
+	req.Header.Set("Content-Type", "application/json")
+	recorder := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(recorder)
+	c.Request = req
+
+	NewAgentHandler(db, nil, nil).ReceiveReport(c)
+	if recorder.Code != http.StatusOK {
+		t.Fatalf("上报返回码 = %d, body=%s", recorder.Code, recorder.Body.String())
+	}
+
+	var gotServer model.Server
+	if err := db.Take(&gotServer, server.ID).Error; err != nil {
+		t.Fatalf("读取资产失败: %v", err)
+	}
+	if gotServer.Uptime != 7200 {
+		t.Fatalf("心跳运行时长未写入资产: got=%d want=7200", gotServer.Uptime)
+	}
+}
+
 func TestGetLatestReportsUsesUTCTimeBoundary(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 	db, err := gorm.Open(sqlite.Open("file:agent_latest_utc?mode=memory&cache=shared"), &gorm.Config{