feat: add signed PostgreSQL release updates

oa-backend/src/main/java/com/kaidi/oa/domain/ContentPieceVersion.java

@@ -5,7 +5,6 @@ import jakarta.persistence.Entity;
 import jakarta.persistence.GeneratedValue;
 import jakarta.persistence.GenerationType;
 import jakarta.persistence.Id;
-import jakarta.persistence.Lob;
 import jakarta.persistence.Table;
 
 import java.time.Instant;
@@ -46,8 +45,7 @@ public class ContentPieceVersion {
     private String titleSnapshot;
 
     /** 正文快照（完整内容，用于 diff 对比）。 */
-    @Lob
-    @Column(name = "body_snapshot")
+    @Column(name = "body_snapshot", columnDefinition = "TEXT")
     private String bodySnapshot;
 
     private Instant createdAt;