feat: session content sync trigger and newest-season selection

Add seasonRefreshProvider (once-per-session FutureProvider) and activeSeason()
helper; HomeScreen listens and invalidates seasonsProvider when new packs arrive;
season_map_screen and season_title_screen switch from list.first to activeSeason.

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

lib/state/providers.dart

@@ -44,6 +44,16 @@ final seasonsProvider = FutureProvider<List<SeasonPack>>(
   (ref) => ref.read(contentRepositoryProvider).availableSeasons(),
 );
 
+/// One background content sync per app session. Home listens and refreshes
+/// the season list when new packs arrived.
+final seasonRefreshProvider = FutureProvider<bool>(
+  (ref) => ref.read(contentRepositoryProvider).refresh(),
+);
+
+/// The season players land in by default: the newest available.
+/// (availableSeasons is sorted by seasonId ascending.)
+SeasonPack activeSeason(List<SeasonPack> seasons) => seasons.last;
+
 final streakProvider = NotifierProvider<StreakNotifier, StreakState>(
   StreakNotifier.new,
 );