feat: Implement notification service and integrate with user interactions

- Added notification service to handle sending and listing notifications.
- Integrated notification sending on user follow and order payment events.
- Updated user service to include fetching followed tenants.
- Enhanced content service to manage access control for content assets.
- Implemented logic for listing content topics based on genre.
- Updated creator service to manage content updates and pricing.
- Improved order service to include detailed order information and notifications.
- Added tests for notification CRUD operations and order details.

backend/app/services/common.go

@@ -74,3 +74,11 @@ func (s *common) Upload(ctx context.Context, file *multipart.FileHeader, typeArg
 		MimeType: file.Header.Get("Content-Type"),
 	}, nil
 }
+
+func (s *common) GetAssetURL(objectKey string) string {
+	// In future: Implement real S3 presigned URL generation here
+	if objectKey == "" {
+		return ""
+	}
+	return "http://mock-storage/" + objectKey
+}