Wire season flow: map screen, progress save, win recording, next stage

SaveRepository (versioned JSON over prefs) with best-result merging and
unlock walking; ContentRepository loads the bundled pack; SeasonFlow/
Progress notifiers orchestrate stage start -> win record -> advance.
Season map grid with stars/locks, Home -> Map -> Game navigation,
close button, next-stage action on the win overlay.

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

lib/l10n/app_en.arb

@@ -11,5 +11,6 @@
   "watchAdContinue": "Continue (ad)",
   "plusFiveMoves": "+5 moves (ad)",
   "giveUp": "Give up",
-  "playAgain": "Play again"
+  "playAgain": "Play again",
+  "nextStage": "Next stage"
 }

lib/l10n/app_ko.arb

@@ -11,5 +11,6 @@
   "watchAdContinue": "광고 보고 이어하기",
   "plusFiveMoves": "+5 이동 (광고)",
   "giveUp": "포기하기",
-  "playAgain": "다시 하기"
+  "playAgain": "다시 하기",
+  "nextStage": "다음 스테이지"
 }