Enhance notification entity and service for improved delivery channel handling

- Introduced new event types for notifications, including email and push, to support a broader range of delivery methods.
- Added a `persistedEventType` function to map delivery channels to their corresponding event types, improving clarity and maintainability.
- Updated the `sendToRecipient` method to ensure in-app notifications are always persisted, enhancing the reliability of notification records.
- Improved error logging for in-app notification persistence failures, providing better context for debugging.

This update enhances the notification system's flexibility and reliability by supporting multiple delivery channels and improving error handling.

internal/notification/service.go

@@ -99,7 +99,18 @@ func (s *notificationService) Send(ctx context.Context, req *NotificationRequest
 }
 
 func (s *notificationService) sendToRecipient(ctx context.Context, recipient notificationRecipient, req *NotificationRequest, link, image string) {
+	// Always persist an in-app record so every send appears in the notification center.
+	if err := s.persistNotification(ctx, recipient, req, link, image, DeliveryChannelInApp); err != nil {
+		s.logger.Error("Failed to persist in-app notification", map[string]interface{}{
+			"error":   err.Error(),
+			"user_id": recipient.UserID,
+		})
+	}
+
 	for _, channel := range req.Channels {
+		if channel == DeliveryChannelInApp {
+			continue
+		}
 		if err := s.persistNotification(ctx, recipient, req, link, image, channel); err != nil {
 			s.logger.Error("Failed to persist notification", map[string]interface{}{
 				"error":   err.Error(),
@@ -153,9 +164,12 @@ func (s *notificationService) sendToRecipient(ctx context.Context, recipient not
 }
 
 func (s *notificationService) persistNotification(ctx context.Context, recipient notificationRecipient, req *NotificationRequest, link, image string, channel DeliveryChannel) error {
-	methods := map[string]string{}
-	eventType := string(channel)
+	eventType, ok := persistedEventType(channel)
+	if !ok {
+		return nil
+	}
 
+	methods := map[string]string{}
 	switch channel {
 	case DeliveryChannelEmail:
 		if recipient.Email == "" {
@@ -168,10 +182,7 @@ func (s *notificationService) persistNotification(ctx context.Context, recipient
 		}
 		methods["push"] = recipient.DeviceTokens[0]
 	case DeliveryChannelInApp:
-		eventType = EventTypeInApp
 		methods["in_app"] = "true"
-	default:
-		return nil
 	}
 
 	status := string(DeliveryStatusSent)