feat(iap): persist adsRemoved flag (additive, saveVersion 1)

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

lib/data/save_repository.dart

@@ -39,6 +39,9 @@ class SaveRepository {
               false;
       _endlessBest =
           (json['endless'] as Map<String, dynamic>?)?['best'] as int? ?? 0;
+      _adsRemoved =
+          (json['flags'] as Map<String, dynamic>?)?['adsRemoved'] as bool? ??
+              false;
     }
   }
 
@@ -52,16 +55,23 @@ class SaveRepository {
   StreakState _streak = StreakState.initial;
   bool _tutorialDone = false;
   int _endlessBest = 0;
+  bool _adsRemoved = false;
 
   StreakState get streak => _streak;
   bool get tutorialDone => _tutorialDone;
   int get endlessBest => _endlessBest;
+  bool get adsRemoved => _adsRemoved;
 
   Future<void> markTutorialDone() {
     _tutorialDone = true;
     return _flush();
   }
 
+  Future<void> setAdsRemoved(bool value) {
+    _adsRemoved = value;
+    return _flush();
+  }
+
   Future<void> recordEndlessScore(int score) {
     if (score > _endlessBest) _endlessBest = score;
     return _flush();
@@ -130,7 +140,7 @@ class SaveRepository {
             'best': _streak.best,
             'lastYmd': _streak.lastYmd,
           },
-          'flags': {'tutorialDone': _tutorialDone},
+          'flags': {'tutorialDone': _tutorialDone, 'adsRemoved': _adsRemoved},
           'endless': {'best': _endlessBest},
         }),
       );