Scaffold Block Seasons Flutter app

flutter create (com.airkjw.blockseasons, iOS+Android), Riverpod,
shared_preferences, audioplayers, gen-l10n EN/KO wiring, app shell
with Home -> Game placeholder.

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

l10n.yaml

@@ -0,0 +1,7 @@
+arb-dir: lib/l10n
+output-dir: lib/l10n/gen
+template-arb-file: app_en.arb
+output-localization-file: app_localizations.dart
+output-class: AppLocalizations
+synthetic-package: false
+nullable-getter: true