[management] Expire unvalidated custom domain registrations (#7497)

Prevent unvalidated registrations from reserving domain names indefinitely.

Give pending registrations a 48-hour validation window and clean up expired entries at startup and every 60 minutes. Emit CustomDomainValidationExpired for each deletion and preserve registrations referenced by services.

Reject validation after expiry and prevent concurrent validation from recreating deleted registrations. Normalize domain names with the shared parser before registration.

Migrate existing pending registrations to receive a fresh 48-hour validation window.

management/internals/server/server.go

@@ -66,7 +66,8 @@ type BaseServer struct {
 	disableLegacyManagementPort bool
 	autoResolveDomains          bool
 
-	proxyAuthClose func()
+	proxyAuthClose    func()
+	domainCleanupStop func()
 
 	// grpcExtensions holds additional gRPC services, interceptors, and shutdown
 	// hooks registered by external modules via RegisterGRPCExtension. Populated
@@ -227,9 +228,26 @@ func (s *BaseServer) Start(ctx context.Context) error {
 	s.update.SetOnUpdateListener(func() {
 		log.WithContext(ctx).Infof("your management version, \"%s\", is outdated, a new management version is available. Learn more here: https://github.com/netbirdio/netbird/releases", version.NetbirdVersion())
 	})
+	s.startDomainCleanup(srvCtx)
 
 	return nil
 }
+func (s *BaseServer) startDomainCleanup(ctx context.Context) {
+	if s.domainCleanupStop != nil {
+		return
+	}
+	mgr := s.ReverseProxyDomainManager()
+	ctx, cancel := context.WithCancel(ctx)
+	done := make(chan struct{})
+	s.domainCleanupStop = func() {
+		cancel()
+		<-done
+	}
+	go func() {
+		defer close(done)
+		mgr.RunValidationCleanup(ctx)
+	}()
+}
 
 // setupTLS resolves the listener's TLS source: an injected config wins over the HttpConfig certificate settings
 func (s *BaseServer) setupTLS(ctx context.Context) (bool, error) {
@@ -260,6 +278,9 @@ func (s *BaseServer) setupTLS(ctx context.Context) (bool, error) {
 func (s *BaseServer) Stop() error {
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 	defer cancel()
+	if s.domainCleanupStop != nil {
+		s.domainCleanupStop()
+	}
 
 	s.IntegratedValidator().Stop(ctx)
 	if s.GeoLocationManager() != nil {