feat: add monitoring agent (Go) + agent report API + cloud billing UI

- Go agent: CPU/mem/disk/port collectors, HTTP report, static binary
- Cross-compile: linux/amd64 + linux/arm64 (statically linked)
- One-line install script for all Linux distros
- Backend: POST /api/v1/agent/report (no JWT) + GET /agent/latest,history (JWT)
- CloudBilling.tsx: fixed syntax errors, stats/trends/records/alerts
- K8s menu renamed to Kubernetes管理

Signed-off-by: Logan.Li

backend/internal/api/routes/routes.go

@@ -289,4 +289,17 @@ func Register(r *gin.Engine, db *gorm.DB, log *zap.Logger, cfg *config.Config) {
 		audit.GET("/statistics", auditHandler.GetAuditStatistics)
 		audit.POST("/logs/clear", auditHandler.ClearAuditLogs)
 	}
+
+	// Agent 上报路由（无需 JWT，使用 Agent Token 鉴权）
+	agentHandler := handlers.NewAgentHandler(db)
+	agentGroup := api.Group("/agent")
+	{
+		agentGroup.POST("/report", agentHandler.ReceiveReport)
+	}
+	// Agent 数据查询（需要 JWT）
+	agentQuery := authorized.Group("/agent")
+	{
+		agentQuery.GET("/latest", agentHandler.GetLatestReports)
+		agentQuery.GET("/history/:hostname", agentHandler.GetHostHistory)
+	}
 }