feat : user 엔티티 해시코드 오버라이딩 추가

Author: seungwookc97

src/main/java/com/back/domain/user/entity/User.java

@@ -14,6 +14,7 @@
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
+import java.util.Objects;
 
 @Entity
 @Table(name = "users")  // 예약어 충돌 방지를 위해 "users" 권장
@@ -70,6 +71,17 @@ public class User {
     @OneToMany(mappedBy = "user", cascade = CascadeType.ALL, orphanRemoval = true)
     private List<PostLike> postLikes = new ArrayList<>();
 
+    @Override
+    public boolean equals(Object o) {
+        if (o == null || getClass() != o.getClass()) return false;
+        User user = (User) o;
+        return Objects.equals(id, user.id);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hashCode(id);
+    }
 
     public boolean isAdmin() {
         return "ADMIN".equalsIgnoreCase(role);