ui(results): groupings empty state uses the UI kit empty state (#1162)

Author: ZhuchkaTriplesix

lib/features/workspace/data_grid_groupings_view.dart

@@ -100,8 +100,11 @@ class _DataGridGroupingsViewState
   @override
   material.Widget build(material.BuildContext context) {
     if (widget.columns.isEmpty || widget.rows.isEmpty) {
-      return material.Center(
-        child: const Text('No data available for grouping.').muted(),
+      return const material.Center(
+        child: QueryaEmptyState(
+          title: 'No data to group',
+          description: 'Run a query that returns rows, then group them here.',
+        ),
       );
     }
 

test/features/workspace/data_grid_groupings_view_test.dart

@@ -26,7 +26,7 @@ void main() {
       );
       await tester.pumpAndSettle();
 
-      expect(find.text('No data available for grouping.'), findsOneWidget);
+      expect(find.text('No data to group'), findsOneWidget);
     });
 
     testWidgets('renders grouping categories and allows aggregation switching', (tester) async {