feat: analytics abstraction with debug backend and game event wiring

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/state/providers.dart

@@ -4,6 +4,7 @@ import '../data/content_repository.dart';
 import '../data/save_repository.dart';
 import '../data/streak.dart';
 import '../game/models/season.dart';
+import '../services/analytics_service.dart';
 import '../services/audio_service.dart';
 import 'endless_best_notifier.dart';
 import 'game_session_notifier.dart';
@@ -66,6 +67,10 @@ final endlessBestProvider = NotifierProvider<EndlessBestNotifier, int>(
   EndlessBestNotifier.new,
 );
 
+final analyticsProvider = Provider<AnalyticsService>(
+  (ref) => AnalyticsService(DebugAnalyticsBackend()),
+);
+
 /// 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) {

lib/state/season_flow_notifier.dart

@@ -23,6 +23,10 @@ class SeasonFlowNotifier extends Notifier<SeasonFlow?> {
   void startSeasonStage(SeasonPack pack, int index) {
     state = SeasonFlow(pack: pack, index: index);
     ref.read(gameSessionProvider.notifier).startStage(pack.stages[index]);
+    ref.read(analyticsProvider).stageStart(
+          seasonId: pack.seasonId,
+          stageId: pack.stages[index].id,
+        );
   }
 
   Future<void> recordWin({required int stars, required int score}) async {

lib/state/tutorial_notifier.dart

@@ -25,16 +25,17 @@ class TutorialNotifier extends Notifier<TutorialStep?> {
 
   Future<void> dismissHud() async {
     if (state != TutorialStep.explainHud) return;
-    await _finish();
+    await _finish(skipped: false);
   }
 
   Future<void> skip() async {
     if (state == null) return;
-    await _finish();
+    await _finish(skipped: true);
   }
 
-  Future<void> _finish() async {
+  Future<void> _finish({required bool skipped}) async {
     state = null;
+    ref.read(analyticsProvider).tutorialFinished(skipped: skipped);
     await ref.read(saveRepositoryProvider).markTutorialDone();
   }
 }