Enhance Notification and User Services with Improved Error Handling and Data Consistency

- Updated GetByID methods in user and customer services to return specific "not found" errors for better clarity in error responses.
- Modified NotificationResponse structure to include a new Recipient field, allowing for more flexible recipient handling.
- Changed CreatedAt and UpdatedAt fields in NotificationResponse to use Unix timestamps (int64) for consistency across the application.
- Improved notification retrieval logic to handle potential nil values for user and customer lookups, ensuring robust data handling.

internal/user/service.go

@@ -245,6 +245,13 @@ func (s *userService) UpdateStatus(ctx context.Context, id string, form *UpdateU
 func (s *userService) GetUserByID(ctx context.Context, id string) (*UserResponse, error) {
 	user, err := s.repository.GetByID(ctx, id)
 	if err != nil {
+		if err.Error() == "user not found" {
+			return nil, errors.New("user not found")
+		}
+		s.logger.Error("Failed to get user by ID", map[string]interface{}{
+			"error":   err.Error(),
+			"user_id": id,
+		})
 		return nil, err
 	}