feat(fixes): some fixes breaking build

internal/database/user_repository.go

@@ -1,4 +1,3 @@
-// File: backend/internal/database/user_repository.go
 package database
 
 import (
@@ -60,7 +59,6 @@ func (r *UserRepository) CreateUserTx(ctx context.Context, user *models.User) er
 }
 
 var (
-	ErrUserExists   = errors.New("user with this username or email already exists")
 	ErrUserNotFound = errors.New("user not found") // Новая ошибка
 )