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>

lib/data/save_repository.dart

@@ -48,6 +48,9 @@ class SaveRepository {
       _musicEnabled =
           (json['flags'] as Map<String, dynamic>?)?['musicEnabled'] as bool? ??
               true;
+      _reviewRequested = (json['flags']
+              as Map<String, dynamic>?)?['reviewRequested'] as bool? ??
+          false;
     }
   }
 
@@ -64,6 +67,7 @@ class SaveRepository {
   bool _adsRemoved = false;
   bool _soundEnabled = true;
   bool _musicEnabled = true;
+  bool _reviewRequested = false;
 
   StreakState get streak => _streak;
   bool get tutorialDone => _tutorialDone;
@@ -72,6 +76,14 @@ class SaveRepository {
   bool get soundEnabled => _soundEnabled;
   bool get musicEnabled => _musicEnabled;
 
+  /// Whether we've already asked the player for a store review (one-time).
+  bool get reviewRequested => _reviewRequested;
+
+  /// Distinct stages the player has cleared (any season, >=1 star). Used to
+  /// gate the review prompt behind a player who is clearly invested.
+  int get stagesClearedCount =>
+      _progress.values.where((p) => p.stars > 0).length;
+
   Future<void> markTutorialDone() {
     _tutorialDone = true;
     return _flush();
@@ -92,6 +104,11 @@ class SaveRepository {
     return _flush();
   }
 
+  Future<void> markReviewRequested() {
+    _reviewRequested = true;
+    return _flush();
+  }
+
   Future<void> recordEndlessScore(int score) {
     if (score > _endlessBest) _endlessBest = score;
     return _flush();
@@ -165,6 +182,7 @@ class SaveRepository {
             'adsRemoved': _adsRemoved,
             'soundEnabled': _soundEnabled,
             'musicEnabled': _musicEnabled,
+            'reviewRequested': _reviewRequested,
           },
           'endless': {'best': _endlessBest},
         }),