feat: implement cross-node event broadcasting with NATSEventBus

- Add UpdateVersionCache method to JetStreamEventStore for cache synchronization
- Add SubscribeToEventStored convenience helper to NATSEventBus
- Create integration tests for cross-node broadcasting scenarios
- Add example demonstrating NATSEventBus + JetStreamEventStore integration

nats_eventbus.go

@@ -210,6 +210,26 @@ func (neb *NATSEventBus) Publish(namespaceID string, event *Event) {
 	}
 }
 
+// SubscribeToEventStored creates a subscription specifically for EventStored events.
+// This is a convenience method for the common pattern of listening to persisted events
+// to update version cache or trigger other actions.
+//
+// Example:
+//
+//	eventStoredCh := natsBus.SubscribeToEventStored("tenant-abc")
+//	go func() {
+//		for event := range eventStoredCh {
+//			actorID := event.Data["actorId"].(string)
+//			version := int64(event.Data["version"].(float64))
+//			store.UpdateVersionCache(actorID, version)
+//		}
+//	}()
+func (neb *NATSEventBus) SubscribeToEventStored(namespacePattern string) <-chan *Event {
+	return neb.SubscribeWithFilter(namespacePattern, &SubscriptionFilter{
+		EventTypes: []string{EventTypeEventStored},
+	})
+}
+
 // Stop closes the NATS event bus and all subscriptions
 func (neb *NATSEventBus) Stop() {
 	neb.mutex.Lock()