fix: auth flow fixed, add getOrCreate method for user

internal/usecase/auth_service.go

@@ -98,16 +98,14 @@ func (s *authService) Authenticate(ctx context.Context, pubKey string, signature
 		return nil, fmt.Errorf("failed to delete challenge: %w", err)
 	}
 
-	user, err := s.userRepo.GetByPubKey(ctx, pubKey)
+	user, err := s.userRepo.GetOrCreateUserByPubKey(ctx, pubKey)
 	if err != nil {
-		return nil, err
-	}
-	if user == nil {
-		return nil, domain.ErrUserNotFound
+		return nil, fmt.Errorf("failed to get or create user: %w", err)
 	}
+
 	user.UpdateLastLogin()
 	if err := s.userRepo.Update(ctx, user); err != nil {
-		return nil, err
+		return nil, fmt.Errorf("failed to update user: %w", err)
 	}
 
 	expiresAt := time.Now().Add(time.Duration(s.cfg.TokenExpMinutes) * time.Minute)