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>

lib/l10n/app_en.arb

@@ -0,0 +1,7 @@
+{
+  "@@locale": "en",
+  "appTitle": "Block Seasons",
+  "play": "Play",
+  "settings": "Settings",
+  "comingSoon": "Coming soon"
+}