feat: enhance v2 components and entity join functionality

- Add entity join controller/routes enhancements
- Improve table management and category value services
- Update v2 table list, card display, search widget components
- Improve split panel layout responsiveness

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend-node/src/controllers/entityJoinController.ts

@@ -561,6 +561,34 @@ export class EntityJoinController {
       });
     }
   }
+  /**
+   * 테이블 컬럼의 고유값 목록 조회 (헤더 필터 드롭다운용)
+   * GET /api/table-management/tables/:tableName/column-values/:columnName
+   */
+  async getColumnUniqueValues(req: Request, res: Response): Promise<void> {
+    try {
+      const { tableName, columnName } = req.params;
+      const companyCode = (req as any).user?.companyCode;
+
+      const data = await tableManagementService.getColumnDistinctValues(
+        tableName,
+        columnName,
+        companyCode
+      );
+
+      res.status(200).json({
+        success: true,
+        data,
+      });
+    } catch (error) {
+      logger.error(`컬럼 고유값 조회 실패: ${req.params.tableName}.${req.params.columnName}`, error);
+      res.status(500).json({
+        success: false,
+        message: "컬럼 고유값 조회 중 오류가 발생했습니다.",
+        error: error instanceof Error ? error.message : "Unknown error",
+      });
+    }
+  }
 }
 
 export const entityJoinController = new EntityJoinController();