layer1: add namespace manager summary

pkg/utils/namespace_manager_model.go

@@ -73,6 +73,12 @@ type NamespaceEvent struct {
 	ObservedAt time.Time
 }
 
+type NamespaceManagerSummary struct {
+	TotalNamespaces int
+	PhaseCounts     map[NamespacePhase]int
+	Subscribers     []string
+}
+
 func NewNamespaceEvent(eventType NamespaceEventType, name string, labels map[string]string, source NamespaceSource, observedAt time.Time) NamespaceEvent {
 	return NamespaceEvent{
 		Type:       eventType,