feat: add signed PostgreSQL release updates

oa-backend/src/main/java/com/kaidi/oa/domain/Discussion.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;
@@ -28,7 +27,6 @@ public class Discussion {
 
     private String category;
 
-    @Lob
     @Column(columnDefinition = "TEXT")
     private String content;
 
@@ -37,7 +35,6 @@ public class Discussion {
     private Instant createdAt;
 
     /** 回帖列表 JSON 数组：[{author, content, createdAt}]。 */
-    @Lob
     @Column(columnDefinition = "TEXT")
     private String repliesJson;