refactor: UniversalListPage externalIsLoading 지원 및 스켈레톤 개선

- UniversalListPage에 externalIsLoading prop 추가
- CardTransactionDetailClient DevFill 자동입력 기능 추가
- 여러 컴포넌트 로딩 상태 처리 개선
- skeleton 컴포넌트 확장

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/components/board/BoardManagement/BoardDetailClientV2.tsx

@@ -15,7 +15,7 @@ import { BoardForm } from './BoardForm';
 import { getBoardById, createBoard, updateBoard, deleteBoard } from './actions';
 import { forceRefreshMenus } from '@/lib/utils/menuRefresh';
 import type { Board, BoardFormData } from './types';
-import { ContentLoadingSpinner } from '@/components/ui/loading-spinner';
+import { DetailPageSkeleton } from '@/components/ui/skeleton';
 import { ErrorCard } from '@/components/ui/error-card';
 import { Button } from '@/components/ui/button';
 import { DeleteConfirmDialog } from '@/components/ui/confirm-dialog';
@@ -197,7 +197,7 @@ export function BoardDetailClientV2({ boardId, initialMode }: BoardDetailClientV
 
   // 로딩 중
   if (isLoading) {
-    return <ContentLoadingSpinner text="게시판 정보를 불러오는 중..." />;
+    return <DetailPageSkeleton sections={1} fieldsPerSection={6} />;
   }
 
   // 에러 발생 (view/edit 모드에서)