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/ui/screens/season_title_screen.dart

@@ -63,7 +63,7 @@ class _SeasonTitleScreenState extends ConsumerState<SeasonTitleScreen> {
           _auto?.cancel();
           _auto = Timer(const Duration(milliseconds: 1600), _go);
         }
-        final pack = list.first;
+        final pack = activeSeason(list);
         final locale = Localizations.localeOf(context).languageCode;
         final number = int.tryParse(pack.seasonId.split('_').last) ?? 1;
         return GestureDetector(