fix(ads): reset ad round in startStage so nextStage advance counts (review fix)

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

lib/state/game_session_notifier.dart

@@ -68,6 +68,7 @@ class GameSessionNotifier extends Notifier<GameViewState?> {
     _engine = GameEngine(stage, attempt: attempt, generator: generator);
     _fxTick = 0;
     _publish(lastPlacement: null);
+    ref.read(adServiceProvider).onRoundStart();
   }
 
   /// Restarts the current stage as a new attempt (fresh piece sequence).
@@ -75,7 +76,6 @@ class GameSessionNotifier extends Notifier<GameViewState?> {
     final stage = _stage;
     if (stage == null) throw StateError('no stage to restart');
     startStage(stage, attempt: _attempt + 1, generator: _generatorOverride);
-    ref.read(adServiceProvider).onRoundStart();
     if (stage.endless) {
       ref.read(analyticsProvider).endlessStart();
     } else {

lib/ui/screens/game_screen.dart

@@ -117,7 +117,6 @@ class _GameScreenState extends ConsumerState<GameScreen>
 
   void _onSessionChange(GameViewState? prev, GameViewState? next) {
     if (next == null) return;
-    if (prev == null) ref.read(adServiceProvider).onRoundStart();
     final audio = ref.read(audioServiceProvider);
     if (prev?.fxTick != next.fxTick && next.lastPlacement != null) {
       final placement = next.lastPlacement!;