Add post change log tracking

backend/src/main/java/com/openisle/model/PostChangeLog.java

@@ -0,0 +1,37 @@
+package com.openisle.model;
+
+import jakarta.persistence.*;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+import org.hibernate.annotations.CreationTimestamp;
+
+import java.time.LocalDateTime;
+
+@Getter
+@Setter
+@NoArgsConstructor
+@Entity
+@Table(name = "post_change_logs")
+@Inheritance(strategy = InheritanceType.JOINED)
+public abstract class PostChangeLog {
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    @ManyToOne(fetch = FetchType.LAZY, optional = false)
+    @JoinColumn(name = "post_id")
+    private Post post;
+
+    @ManyToOne(fetch = FetchType.LAZY, optional = false)
+    @JoinColumn(name = "user_id")
+    private User user;
+
+    @CreationTimestamp
+    @Column(nullable = false, updatable = false)
+    private LocalDateTime createdAt;
+
+    @Enumerated(EnumType.STRING)
+    @Column(nullable = false)
+    private PostChangeType type;
+}