feat: endless mode UI - game over card, best score, HUD

lib/state/providers.dart

@@ -5,6 +5,7 @@ import '../data/save_repository.dart';
 import '../data/streak.dart';
 import '../game/models/season.dart';
 import '../services/audio_service.dart';
+import 'endless_best_notifier.dart';
 import 'game_session_notifier.dart';
 import 'progress_notifier.dart';
 import 'season_flow_notifier.dart';
@@ -51,6 +52,10 @@ final tutorialProvider = NotifierProvider<TutorialNotifier, TutorialStep?>(
   TutorialNotifier.new,
 );
 
+final endlessBestProvider = NotifierProvider<EndlessBestNotifier, int>(
+  EndlessBestNotifier.new,
+);
+
 /// The visual theme of whatever season is in play; fallback outside seasons
 /// (home, endless). Pure model — UI converts via ThemeColors.
 final activeThemeProvider = Provider<SeasonTheme>((ref) {