fix(l10n): localize line-bomb row/column chooser labels

The line-bomb axis chooser hardcoded Korean 가로/세로; route them through
new boosterLineRow/boosterLineCol keys (EN: Row/Column).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/l10n/app_en.arb

@@ -70,5 +70,7 @@
   "dailyClaim": "Claim",
   "dailyDoubleWithAd": "Watch ad for 2×",
   "boosterTapTarget": "Tap a cell",
-  "boosterTapLine": "Tap a row or column"
+  "boosterTapLine": "Tap a row or column",
+  "boosterLineRow": "Row",
+  "boosterLineCol": "Column"
 }

lib/l10n/app_ko.arb

@@ -42,5 +42,7 @@
   "dailyClaim": "받기",
   "dailyDoubleWithAd": "광고 보고 2배",
   "boosterTapTarget": "칸을 선택하세요",
-  "boosterTapLine": "줄을 선택하세요"
+  "boosterTapLine": "줄을 선택하세요",
+  "boosterLineRow": "가로",
+  "boosterLineCol": "세로"
 }

lib/ui/screens/game_screen.dart

@@ -195,11 +195,11 @@ class _GameScreenState extends ConsumerState<GameScreen>
         actions: [
           TextButton(
             onPressed: () => Navigator.of(context).pop(_LineAxis.row),
-            child: const Text('↔ 가로'),
+            child: Text('↔ ${l10n.boosterLineRow}'),
           ),
           TextButton(
             onPressed: () => Navigator.of(context).pop(_LineAxis.col),
-            child: const Text('↕ 세로'),
+            child: Text('↕ ${l10n.boosterLineCol}'),
           ),
         ],
       ),