feat: season title card on cold start

Shows "SEASON 1 / First Bloom / N stages" over the season background for
~1.6s between splash and home; tap anywhere skips. Bails to home on
content-load error. Adds seasonLabel/seasonStages l10n keys (en + ko).

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

lib/l10n/app_ko.arb

@@ -14,5 +14,7 @@
   "playAgain": "다시 하기",
   "nextStage": "다음 스테이지",
   "streakMilestone": "{days}일 연속 플레이! 대단해요!",
-  "almostThere": "{percent}% 달성!"
+  "almostThere": "{percent}% 달성!",
+  "seasonLabel": "SEASON",
+  "seasonStages": "{count}개 스테이지"
 }