refactor: [shitty claude AI first try] restructure server and user services, add new test cases, and improve error handling

internal/api/user/repo/user_repo.go

@@ -40,13 +40,6 @@ func (u userRepo) GetUserByUuid(ctx context.Context, requestUuid string) (*db.Us
 	return &dbUser, nil
 }
 
-func userFromDbToDomain(dbUser db.User) *domain.User {
-	return &domain.User{
-		PhoneNumber: dbUser.PhoneNumber,
-		Uuid:        dbUser.Uuid.String(),
-	}
-}
-
 func (u userRepo) CreateUser(ctx context.Context, phoneNumber string) (*db.User, error) {
 	queries := db.New(u.db)
 	user, err := queries.CreateUser(ctx, phoneNumber)