feat: add tag timeline and summary sections

src/main/java/com/openisle/model/Tag.java

@@ -4,6 +4,10 @@ import jakarta.persistence.*;
 import lombok.Getter;
 import lombok.NoArgsConstructor;
 import lombok.Setter;
+import org.hibernate.annotations.CreationTimestamp;
+
+import java.time.LocalDateTime;
+
 
 @Entity
 @Getter
@@ -29,4 +33,13 @@ public class Tag {
 
     @Column(nullable = false)
     private boolean approved = true;
+
+    @CreationTimestamp
+    @Column(nullable = false, updatable = false,
+            columnDefinition = "DATETIME(6) DEFAULT CURRENT_TIMESTAMP(6)")
+    private LocalDateTime createdAt;
+
+    @ManyToOne(fetch = FetchType.LAZY)
+    @JoinColumn(name = "creator_id")
+    private User creator;
 }