feat: persist tutorial completion and endless best score

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

lib/data/save_repository.dart

@@ -34,6 +34,11 @@ class SaveRepository {
           lastYmd: streak['lastYmd'] as String?,
         );
       }
+      _tutorialDone =
+          (json['flags'] as Map<String, dynamic>?)?['tutorialDone'] as bool? ??
+              false;
+      _endlessBest =
+          (json['endless'] as Map<String, dynamic>?)?['best'] as int? ?? 0;
     }
   }
 
@@ -45,8 +50,22 @@ class SaveRepository {
   final SharedPreferences _prefs;
   final Map<String, StageProgress> _progress = {};
   StreakState _streak = StreakState.initial;
+  bool _tutorialDone = false;
+  int _endlessBest = 0;
 
   StreakState get streak => _streak;
+  bool get tutorialDone => _tutorialDone;
+  int get endlessBest => _endlessBest;
+
+  Future<void> markTutorialDone() {
+    _tutorialDone = true;
+    return _flush();
+  }
+
+  Future<void> recordEndlessScore(int score) {
+    if (score > _endlessBest) _endlessBest = score;
+    return _flush();
+  }
 
   Future<void> saveStreak(StreakState streak) {
     _streak = streak;
@@ -111,6 +130,8 @@ class SaveRepository {
             'best': _streak.best,
             'lastYmd': _streak.lastYmd,
           },
+          'flags': {'tutorialDone': _tutorialDone},
+          'endless': {'best': _endlessBest},
         }),
       );
 }