refactor(ui): 애니메이션 관련 위젯 개선

- canvas_battle_composer: 레어리티 색상 매핑 연동
- ascii_animation_card: 코드 정리
- enhanced_animation_panel: 테마 상수 적용

lib/src/core/animation/canvas/canvas_battle_composer.dart

@@ -8,6 +8,7 @@ import 'package:asciineverdie/src/core/animation/monster_size.dart';
 import 'package:asciineverdie/src/core/animation/race_character_frames.dart';
 import 'package:asciineverdie/src/core/animation/weapon_category.dart';
 import 'package:asciineverdie/src/core/animation/weapon_effects.dart';
+import 'package:asciineverdie/src/core/animation/canvas/rarity_color_mapper.dart';
 import 'package:asciineverdie/src/core/model/item_stats.dart';
 
 /// Canvas용 전투 프레임 합성기