style(front): 플랫폼별 애니메이션 패널 비율 조정

- 데스크톱/웹: 넓은 비율 (2.5)
- 모바일: 16:9 비율
- HeroVsBossAnimation 레이아웃 Flexible 적용

lib/src/features/front/front_screen.dart

@@ -1,3 +1,6 @@
+import 'dart:io' show Platform;
+
+import 'package:flutter/foundation.dart' show kIsWeb;
 import 'package:flutter/material.dart';
 
 import 'package:asciineverdie/data/game_text_l10n.dart' as game_l10n;
@@ -168,14 +171,23 @@ class _RetroHeader extends StatelessWidget {
 class _AnimationPanel extends StatelessWidget {
   const _AnimationPanel();
 
+  /// 플랫폼별 비율 반환 (데스크톱: 넓게, 모바일: 높게)
+  double _getAspectRatio() {
+    if (kIsWeb) return 2.5; // 웹: 넓은 비율
+    if (Platform.isMacOS || Platform.isWindows || Platform.isLinux) {
+      return 2.5; // 데스크톱: 넓은 비율
+    }
+    return 16 / 9; // 모바일(iOS/Android): 16:9
+  }
+
   @override
   Widget build(BuildContext context) {
     return RetroPanel(
       title: 'BATTLE',
       padding: const EdgeInsets.all(8),
-      child: const AspectRatio(
-        aspectRatio: 16 / 9,
-        child: HeroVsBossAnimation(),
+      child: AspectRatio(
+        aspectRatio: _getAspectRatio(),
+        child: const HeroVsBossAnimation(),
       ),
     );
   }