feat(settings): soundEnabled provider gates SFX and haptics

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test/state/sound_notifier_test.dart

@@ -0,0 +1,21 @@
+import 'package:block_seasons/data/save_repository.dart';
+import 'package:block_seasons/state/providers.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+void main() {
+  test('reads persisted sound flag and toggles + persists', () async {
+    SharedPreferences.setMockInitialValues({});
+    final repo = await SaveRepository.open();
+    final c = ProviderContainer(
+      overrides: [saveRepositoryProvider.overrideWithValue(repo)],
+    );
+    addTearDown(c.dispose);
+
+    expect(c.read(soundEnabledProvider), isTrue);
+    await c.read(soundEnabledProvider.notifier).toggle();
+    expect(c.read(soundEnabledProvider), isFalse);
+    expect(repo.soundEnabled, isFalse);
+  });
+}