feat(ground-suite): add theme selector

ground-suite/test/widget_test.dart

@@ -21,6 +21,16 @@ void main() {
     expect(find.text('Replay fixture'), findsAtLeastNWidgets(1));
     expect(find.text('Vehicle identity'), findsOneWidget);
 
+    await tester.tap(find.byTooltip('Choose theme'));
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Dark'));
+    await tester.pumpAndSettle();
+
+    expect(
+      tester.widget<MaterialApp>(find.byType(MaterialApp)).themeMode,
+      ThemeMode.dark,
+    );
+
     await tester.tap(find.byIcon(Icons.receipt_long_outlined));
     await tester.pumpAndSettle();