회원탈퇴 시 닉네임 앞에 "deleted_"를 추가

src/main/kotlin/kr/co/vividnext/sodalive/member/MemberService.kt

@@ -549,6 +549,7 @@ class MemberService(
 
         logoutAll(memberId = member.id!!)
         member.isActive = false
+        member.nickname = "deleted_${member.nickname}"
 
         val signOut = SignOut(reason = signOutRequest.reason)
         signOut.member = member

src/main/kotlin/kr/co/vividnext/sodalive/member/auth/AuthService.kt

@@ -64,6 +64,7 @@ class AuthService(
     fun signOut(memberId: Long) {
         val member = memberRepository.findByIdOrNull(memberId) ?: throw SodaException("로그인 정보를 확인해주세요.")
         member.isActive = false
+        member.nickname = "deleted_${member.nickname}"
 
         val signOut = SignOut(reason = "운영정책을 위반하여 이용을 제한합니다.")
         signOut.member = member