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>

lib/l10n/app_en.arb

@@ -52,5 +52,7 @@
       }
     }
   },
-  "newBest": "NEW BEST!"
+  "newBest": "NEW BEST!",
+  "adventure": "Adventure",
+  "classic": "Classic"
 }

lib/l10n/app_ko.arb

@@ -24,5 +24,7 @@
   "tutorialHud": "이동 횟수가 끝나기 전에 목표를 달성하세요. 이제 직접!",
   "gameOver": "게임 오버",
   "bestScore": "최고 {score}",
-  "newBest": "신기록!"
+  "newBest": "신기록!",
+  "adventure": "어드벤처",
+  "classic": "클래식"
 }