feat: Enhance entity options retrieval with additional fields support

- Updated the `getEntityOptions` function to accept an optional `fields` parameter, allowing clients to specify additional columns to be retrieved.
- Implemented logic to dynamically include extra columns in the SQL query based on the provided `fields`, improving flexibility in data retrieval.
- Enhanced the response to indicate whether extra fields were included, facilitating better client-side handling of the data.
- Added logging for authentication failures in the `AuthGuard` component to improve debugging and user experience.
- Integrated auto-fill functionality in the `V2Select` component to automatically populate fields based on selected entity references, enhancing user interaction.
- Updated the `ItemSearchModal` to support multi-selection of items, improving usability in item management scenarios.

frontend/components/v2/config-panels/V2SelectConfigPanel.tsx

@@ -302,6 +302,15 @@ export const V2SelectConfigPanel: React.FC<V2SelectConfigPanelProps> = ({ config
               테이블 컬럼을 조회할 수 없습니다. 테이블 타입 관리에서 참조 테이블을 설정해주세요.
             </p>
           )}
+
+          {/* 자동 채움 안내 */}
+          {config.entityTable && entityColumns.length > 0 && (
+            <div className="border-t pt-3">
+              <p className="text-muted-foreground text-[10px]">
+                같은 폼에 참조 테이블({config.entityTable})의 컬럼이 배치되어 있으면, 엔티티 선택 시 해당 필드가 자동으로 채워집니다.
+              </p>
+            </div>
+          )}
         </div>
       )}