Wire season flow: map screen, progress save, win recording, next stage

SaveRepository (versioned JSON over prefs) with best-result merging and
unlock walking; ContentRepository loads the bundled pack; SeasonFlow/
Progress notifiers orchestrate stage start -> win record -> advance.
Season map grid with stars/locks, Home -> Map -> Game navigation,
close button, next-stage action on the win overlay.

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

lib/data/content_repository.dart

@@ -0,0 +1,21 @@
+import 'dart:convert';
+
+import 'package:flutter/services.dart';
+
+import '../game/models/season.dart';
+
+/// Resolves season content. Phase 3: bundled assets only; remote download
+/// and caching land in Phase 4.
+class ContentRepository {
+  static const bundledSeasonIds = ['season_001'];
+
+  Future<SeasonPack> loadBundledSeason(String seasonId) async {
+    final raw =
+        await rootBundle.loadString('assets/seasons/$seasonId/pack.json');
+    return SeasonPack.fromJson(jsonDecode(raw) as Map<String, dynamic>);
+  }
+
+  Future<List<SeasonPack>> availableSeasons() async => [
+        for (final id in bundledSeasonIds) await loadBundledSeason(id),
+      ];
+}