refactor: 아이디 찾기 시 phoneNumberUtil 사용

Author: chominju02

src/main/java/life/mosu/mosuserver/application/user/MyUserService.java

@@ -42,7 +42,7 @@ public ChangePasswordResponse changePassword(ChangePasswordRequest request,
     @Transactional(readOnly = true, propagation = Propagation.SUPPORTS)
     public FindLoginIdResponse findLoginId(FindLoginIdRequest request) {
         UserJpaEntity user = userJpaRepository.findByNameAndPhoneNumber(request.name(),
-                        "U" + request.phoneNumber())
+                        PhoneNumberUtil.formatPhoneNumber(request.phoneNumber()))
                 .orElseThrow(() -> new CustomRuntimeException(ErrorCode.NOT_FOUND_LOGIN_ID));
 
         return FindLoginIdResponse.from(user.getLoginId());