feat(review): request a store review after a 3-star win, once

Adds an in-app review prompt gated by ReviewPromptPolicy: only after a
3-star stage win, once the player has cleared >=5 stages, at most once
ever (persisted reviewRequested flag). ReviewService swallows all
failures and only burns the one-shot when the store actually shows the
sheet, so an unavailable store retries on a later win. StoreReviewer
wraps in_app_review behind a Reviewer seam so unit tests skip platform
channels. 13 new tests; full suite 194 green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/data/save_repository_review_test.dart

@@ -0,0 +1,43 @@
+import 'package:block_seasons/data/save_repository.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  Future<SaveRepository> freshRepo() async {
+    SharedPreferences.setMockInitialValues({});
+    return SaveRepository(await SharedPreferences.getInstance());
+  }
+
+  test('reviewRequested starts false', () async {
+    final repo = await freshRepo();
+    expect(repo.reviewRequested, isFalse);
+  });
+
+  test('markReviewRequested flips the flag and persists across reload', () async {
+    final repo = await freshRepo();
+    await repo.markReviewRequested();
+    expect(repo.reviewRequested, isTrue);
+
+    // A fresh repository over the same prefs must see the saved flag.
+    final reloaded = SaveRepository(await SharedPreferences.getInstance());
+    expect(reloaded.reviewRequested, isTrue);
+  });
+
+  test('stagesClearedCount counts distinct stages cleared with >=1 star',
+      () async {
+    final repo = await freshRepo();
+    expect(repo.stagesClearedCount, 0);
+
+    await repo.recordResult(
+        seasonId: 'season_001', stageId: 's1', stars: 1, score: 100);
+    await repo.recordResult(
+        seasonId: 'season_001', stageId: 's2', stars: 3, score: 300);
+    // Replaying the same stage must not double-count.
+    await repo.recordResult(
+        seasonId: 'season_001', stageId: 's1', stars: 2, score: 500);
+
+    expect(repo.stagesClearedCount, 2);
+  });
+}