fix: 빌더 생성자 허용 범위 변경

Author: lvalentine6

src/main/java/eatda/domain/story/Story.java

@@ -51,7 +51,7 @@ public class Story extends AuditingEntity {
     private String imageKey;
 
     @Builder
-    public Story(
+    private Story(
             Member member,
             String storeKakaoId,
             String storeName,