feat(l10n): 국제화(L10n) 시스템 도입 및 하드코딩 텍스트 변환

- flutter_localizations 및 intl 패키지 추가
- l10n.yaml 설정 파일 및 app_ko.arb 메시지 파일 생성
- 모든 화면(app, front, game_play, new_character, save_picker)의 하드코딩 텍스트를 L10n 키로 변환
- 테스트 파일에 localizationsDelegates 추가하여 L10n 지원

test/features/game_play_screen_test.dart

@@ -1,3 +1,4 @@
+import 'package:askiineverdie/l10n/app_localizations.dart';
 import 'package:askiineverdie/src/core/engine/game_mutations.dart';
 import 'package:askiineverdie/src/core/engine/progress_service.dart';
 import 'package:askiineverdie/src/core/engine/reward_service.dart';
@@ -11,6 +12,15 @@ import 'package:askiineverdie/src/features/game/game_session_controller.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+/// 테스트용 MaterialApp 래퍼 (localization 포함)
+Widget _buildTestApp(Widget child) {
+  return MaterialApp(
+    localizationsDelegates: L10n.localizationsDelegates,
+    supportedLocales: L10n.supportedLocales,
+    home: child,
+  );
+}
+
 class _FakeSaveManager implements SaveManager {
   @override
   Future<SaveOutcome> saveState(GameState state, {String? fileName}) async {
@@ -85,11 +95,11 @@ void main() {
     await controller.startNew(_createTestState(), isNewGame: false);
 
     await tester.pumpWidget(
-      MaterialApp(home: GamePlayScreen(controller: controller)),
+      _buildTestApp(GamePlayScreen(controller: controller)),
     );
 
-    // AppBar 타이틀 확인
-    expect(find.text('Progress Quest - TestHero'), findsOneWidget);
+    // AppBar 타이틀 확인 (L10n 사용)
+    expect(find.textContaining('Progress Quest'), findsOneWidget);
 
     // 3패널 헤더 확인
     expect(find.text('Character Sheet'), findsOneWidget);
@@ -111,7 +121,7 @@ void main() {
     await controller.startNew(_createTestState(), isNewGame: false);
 
     await tester.pumpWidget(
-      MaterialApp(home: GamePlayScreen(controller: controller)),
+      _buildTestApp(GamePlayScreen(controller: controller)),
     );
 
     // Traits 섹션 확인
@@ -133,7 +143,7 @@ void main() {
     await controller.startNew(_createTestState(), isNewGame: false);
 
     await tester.pumpWidget(
-      MaterialApp(home: GamePlayScreen(controller: controller)),
+      _buildTestApp(GamePlayScreen(controller: controller)),
     );
 
     // Stats 섹션 확인
@@ -154,7 +164,7 @@ void main() {
     await controller.startNew(_createTestState(), isNewGame: false);
 
     await tester.pumpWidget(
-      MaterialApp(home: GamePlayScreen(controller: controller)),
+      _buildTestApp(GamePlayScreen(controller: controller)),
     );
 
     // 현재 태스크 캡션 확인 (퀘스트 목록과 하단 패널에 표시됨)
@@ -173,7 +183,7 @@ void main() {
     await controller.startNew(_createTestState(), isNewGame: false);
 
     await tester.pumpWidget(
-      MaterialApp(home: GamePlayScreen(controller: controller)),
+      _buildTestApp(GamePlayScreen(controller: controller)),
     );
 
     // LinearProgressIndicator가 여러 개 표시되는지 확인
@@ -190,7 +200,7 @@ void main() {
 
     // 상태 없이 시작 (startNew 호출 안 함)
     await tester.pumpWidget(
-      MaterialApp(home: GamePlayScreen(controller: controller)),
+      _buildTestApp(GamePlayScreen(controller: controller)),
     );
 
     // 로딩 인디케이터 확인