MOSU-352 fix: 카카오 중복 유저 업데이트 분기

Author: wlgns12370

src/main/java/life/mosu/mosuserver/application/oauth/OAuthUserPersistenceProcessor.java

@@ -23,17 +23,8 @@ public UserJpaEntity process(final OAuthUserInfo info) {
         return userRepository.findByPhoneNumber(
                         PhoneNumberUtil.formatPhoneNumber(info.phoneNumber()))
                 .map(existingUser -> {
-                    switch (existingUser.getProvider()) {
-                        case MOSU:
-                            if (existingUser.isPendingUser()) {
-                                throw new OAuthException("DUPLICATE");
-                            }
-                            break;
-                        case KAKAO:
-                            if (existingUser.isPendingUser()) {
-                                throw new OAuthException("KAKAO_DUPLICATE");
-                            }
-                            break;
+                    if (existingUser.isMosuUser()) {
+                        throw new OAuthException("DUPLICATE");
                     }
                     existingUser.updateOAuthUser(
                             info.gender(),