feat: Optimize batch management and improve performance

- Reduced timeout for RestApiConnector to 20 seconds to ensure timely feedback for previews.
- Implemented caching for external DB metadata to minimize connection overhead and improve response times.
- Enhanced internal DB table and column retrieval with TTL caching to prevent database pool exhaustion.
- Introduced error handling for external DB timeouts, providing clearer feedback to users.
- Updated batch management UI to improve user experience with better error messages and streamlined data handling.

These changes aim to enhance the efficiency and reliability of batch management processes.

backend-node/src/controllers/batchManagementController.ts

@@ -501,12 +501,13 @@ export class BatchManagementController {
       });
 
       // RestApiConnector 사용하여 데이터 조회
+      // 미리보기는 프론트 기본 30초 타임아웃 안에 응답해야 하므로 20초로 제한 — 실패 시 빠르게 피드백
       const { RestApiConnector } = await import("../database/RestApiConnector");
 
       const connector = new RestApiConnector({
         baseUrl: apiUrl,
         apiKey: finalApiKey,
-        timeout: 30000,
+        timeout: 20000,
       });
 
       // 연결 테스트
@@ -600,15 +601,15 @@ export class BatchManagementController {
       }
 
       const data = extractedData.slice(0, 5); // 최대 5개 샘플만
+      // 미리보기 응답 CPU 부담 줄이기 위해 데이터 본문 로깅은 생략 (개수만 기록)
       console.log(
-        `[previewRestApiData] 슬라이스된 데이터 (${extractedData.length}개 중 ${data.length}개):`,
-        data
+        `[previewRestApiData] 샘플 ${data.length}건 추출 (전체 ${extractedData.length}건)`
       );
 
       if (data.length > 0) {
         // 첫 번째 객체에서 필드명 추출
         const fields = Object.keys(data[0]);
-        console.log(`[previewRestApiData] 추출된 필드:`, fields);
+        console.log(`[previewRestApiData] 추출된 필드 수: ${fields.length}`);
 
         return res.json({
           success: true,