feat: 신규 회원 abvDegree 기본값을 5.0%로 변경

Author: MEOHIN

src/main/java/com/back/domain/user/service/UserAuthService.java

@@ -95,7 +95,7 @@ public User joinSocial(String oauthId, String email, String nickname){
         User user = User.builder()
                 .email(email)
                 .nickname(uniqueNickname)
-                .abvDegree(0.0)
+                .abvDegree(5.0)
                 .createdAt(LocalDateTime.now())
                 .updatedAt(LocalDateTime.now())
                 .role("USER")