Fix default creation timestamps

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

@@ -4,6 +4,7 @@ import jakarta.persistence.*;
 import lombok.Getter;
 import lombok.NoArgsConstructor;
 import lombok.Setter;
+import org.hibernate.annotations.CreationTimestamp;
 
 import java.time.LocalDateTime;
 
@@ -42,11 +43,8 @@ public class Notification {
     @Column(name = "is_read", nullable = false)
     private boolean read = false;
 
-    @Column(nullable = false)
+    @CreationTimestamp
+    @Column(nullable = false, updatable = false,
+            columnDefinition = "DATETIME(6) DEFAULT CURRENT_TIMESTAMP(6)")
     private LocalDateTime createdAt;
-
-    @PrePersist
-    protected void onCreate() {
-        this.createdAt = LocalDateTime.now();
-    }
 }