feat: redesigned home with adventure/classic entries and endless best

Add adventure/classic l10n keys; rewrite HomeScreen with SeasonBackground,
2×2 glossy logo mark, Adventure→SeasonMap + Classic→endless GameScreen buttons,
and conditional best-score caption. Update widget_test assertions accordingly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

test/widget_test.dart

@@ -23,6 +23,7 @@ void main() {
     await tester.pumpAndSettle();
 
     expect(find.text('Block Seasons'), findsOneWidget);
-    expect(find.text('Play'), findsOneWidget);
+    expect(find.text('Adventure'), findsOneWidget);
+    expect(find.text('Classic'), findsOneWidget);
   });
 }