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

lib/state/endless_best_notifier.dart

@@ -0,0 +1,18 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import 'providers.dart';
+
+/// Reactive view over SaveRepository's endless best score.
+class EndlessBestNotifier extends Notifier<int> {
+  @override
+  int build() => ref.read(saveRepositoryProvider).endlessBest;
+
+  /// Records the run; returns true when it set a new best.
+  Future<bool> record(int score) async {
+    final repo = ref.read(saveRepositoryProvider);
+    final isNewBest = score > state;
+    await repo.recordEndlessScore(score);
+    state = repo.endlessBest;
+    return isNewBest;
+  }
+}

lib/state/game_session_notifier.dart

@@ -23,6 +23,7 @@ class GameViewState {
     required this.objectiveProgress,
     required this.lastPlacement,
     required this.fxTick,
+    required this.endless,
   });
 
   final GridState grid;
@@ -40,6 +41,8 @@ class GameViewState {
 
   /// Increments on every accepted placement so animations can retrigger.
   final int fxTick;
+
+  final bool endless;
 }
 
 /// Bridges the pure-Dart [GameEngine] to the widget tree. The engine object
@@ -107,7 +110,8 @@ class GameSessionNotifier extends Notifier<GameViewState?> {
       score: engine.score,
       comboStreak: engine.combo.streak,
       movesLeft: engine.movesLeft,
-      moveLimit: engine.movesLeft + engine.movesUsed,
+      endless: engine.endless,
+      moveLimit: engine.endless ? 0 : engine.movesLeft + engine.movesUsed,
       phase: engine.phase,
       stuckReason: engine.stuckReason,
       objectives: engine.objectives,

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) {