Add cleanup, minor fixes

backend/internal/user/service.go

@@ -189,3 +189,9 @@ func (s *Service) ActivateUser(ctx context.Context, user *User) (*User, error) {
 func (s *Service) DeleteUser(ctx context.Context, user *User) error {
 	return s.r.DeleteUser(ctx, user.Id)
 }
+
+// CleanupUsers deletes users that were created but never activated, e.g. when
+// signup failed after the account row was inserted.
+func (s *Service) CleanupUsers(ctx context.Context) error {
+	return s.r.CleanupUsers(ctx)
+}