🐛 fix : 폴더 목록 조회 response itemCount 추가

Author: ramen0519

src/main/java/com/finsight/finsight/domain/storage/application/dto/response/FolderResponse.java

@@ -6,14 +6,28 @@ public record FolderResponse(
         Long folderId,
         String folderType,
         String folderName,
-        Integer sortOrder
+        Integer sortOrder,
+        Long itemCount
 ) {
+    // 폴더 생성용 (itemCount 없이)
     public static FolderResponse from(FolderEntity entity) {
         return new FolderResponse(
                 entity.getFolderId(),
                 entity.getFolderType().name(),
                 entity.getFolderName(),
-                entity.getSortOrder()
+                entity.getSortOrder(),
+                null
+        );
+    }
+
+    // 폴더 조회/수정용 (itemCount 포함)
+    public static FolderResponse from(FolderEntity entity, Long itemCount) {
+        return new FolderResponse(
+                entity.getFolderId(),
+                entity.getFolderType().name(),
+                entity.getFolderName(),
+                entity.getSortOrder(),
+                itemCount
         );
     }
 }