feat(19-04): user authorizer, user.Deleting and handle backfill

Register lighthouse user:{id} if the namespace is free, fire user.Deleting before unscoped delete, and backfill missing handles.

Co-authored-by: Cursor <cursoragent@cursor.com>

controllers/users_admin_controller.go

@@ -522,6 +522,9 @@ func (c usersAdminController) FormAfterDelete(ctx context.Context, model any) er
 	if !ok {
 		return errors.New("users admin: a delete needs its transaction")
 	}
+	if err := FireDeletingEvent(ctx, c.application(), user, tx); err != nil {
+		return fmt.Errorf("%s: %w", classes.DeletingEventName, err)
+	}
 	if err := classes.ForceDeleteCleanup(ctx, tx, c.bucket(), user); err != nil {
 		return err
 	}