fix(animation): ASCII 애니메이션 높낮이/공백 문제 수정

- walkingAnimation, townAnimation 4줄 → 3줄 통일
- character_frames.dart 모든 프레임 폭 6자로 통일
- _compose() 이펙트 Y 위치 동적 계산 (하드코딩 제거)
- withShield() 3줄 캐릭터용으로 수정 (index 3 → index 1)
- BattleComposer 캔버스 시스템 및 배경 합성 추가
- 무기 카테고리별 이펙트, 몬스터 크기/색상 시스템 구현

lib/src/core/animation/background_data.dart

@@ -0,0 +1,178 @@
+// 환경별 배경 패턴 데이터
+// ASCII Patrol 스타일 - 패럴렉스 스크롤링 배경
+
+import 'package:askiineverdie/src/core/animation/background_layer.dart';
+
+/// 환경별 배경 레이어 반환
+List<BackgroundLayer> getBackgroundLayers(EnvironmentType environment) {
+  return switch (environment) {
+    EnvironmentType.town => _townLayers,
+    EnvironmentType.forest => _forestLayers,
+    EnvironmentType.cave => _caveLayers,
+    EnvironmentType.dungeon => _dungeonLayers,
+    EnvironmentType.tech => _techLayers,
+    EnvironmentType.void_ => _voidLayers,
+  };
+}
+
+// ============================================================================
+// 마을 (Town) - 건물 실루엣
+// ============================================================================
+const _townLayers = [
+  // 원경 - 하늘/별
+  BackgroundLayer(
+    lines: [r'. *  .   *  . *  .   *  . *  .   *  '],
+    scrollSpeed: 0.05,
+    yStart: 0,
+  ),
+  // 중경 - 건물 실루엣
+  BackgroundLayer(
+    lines: [
+      r'   _|__|_      _|__|_      _|__|_   ',
+      r'  |      |    |      |    |      |  ',
+    ],
+    scrollSpeed: 0.15,
+    yStart: 1,
+  ),
+  // 전경 - 바닥
+  BackgroundLayer(
+    lines: [r'====[]====[]====[]====[]====[]====[]'],
+    scrollSpeed: 0.3,
+    yStart: 7,
+  ),
+];
+
+// ============================================================================
+// 숲 (Forest) - 나무
+// ============================================================================
+const _forestLayers = [
+  // 원경 - 하늘/별
+  BackgroundLayer(
+    lines: [r'.  *  .    *   .  *  .    *   .  *  '],
+    scrollSpeed: 0.05,
+    yStart: 0,
+  ),
+  // 중경 - 나무 실루엣
+  BackgroundLayer(
+    lines: [
+      r'   ,@@@,          ,@@,           ,@@@',
+      r'  @@   @@        @@  @@         @@   ',
+    ],
+    scrollSpeed: 0.15,
+    yStart: 1,
+  ),
+  // 전경 - 풀/바닥
+  BackgroundLayer(
+    lines: [r'____||____||____||____||____||____||'],
+    scrollSpeed: 0.3,
+    yStart: 7,
+  ),
+];
+
+// ============================================================================
+// 동굴 (Cave) - 바위
+// ============================================================================
+const _caveLayers = [
+  // 천장
+  BackgroundLayer(
+    lines: [r'vvVVvvVVvvVVvvVVvvVVvvVVvvVVvvVVvvVV'],
+    scrollSpeed: 0.1,
+    yStart: 0,
+  ),
+  // 종유석
+  BackgroundLayer(
+    lines: [
+      r'  |       V      |       V      |   ',
+      r'  V              V              V   ',
+    ],
+    scrollSpeed: 0.15,
+    yStart: 1,
+  ),
+  // 바닥 - 석순
+  BackgroundLayer(
+    lines: [r'^__/\__^__/\__^__/\__^__/\__^__/\__^'],
+    scrollSpeed: 0.25,
+    yStart: 7,
+  ),
+];
+
+// ============================================================================
+// 던전 (Dungeon) - 벽돌
+// ============================================================================
+const _dungeonLayers = [
+  // 천장 - 벽돌
+  BackgroundLayer(
+    lines: [r'####|####|####|####|####|####|####|#'],
+    scrollSpeed: 0.1,
+    yStart: 0,
+  ),
+  // 횃불
+  BackgroundLayer(
+    lines: [
+      r'      *           *           *     ',
+      r'     )|          )|          )|     ',
+    ],
+    scrollSpeed: 0.15,
+    yStart: 1,
+  ),
+  // 바닥 - 타일
+  BackgroundLayer(
+    lines: [r'====[]====[]====[]====[]====[]====[]'],
+    scrollSpeed: 0.25,
+    yStart: 7,
+  ),
+];
+
+// ============================================================================
+// 기술 (Tech) - 회로
+// ============================================================================
+const _techLayers = [
+  // 상단 - 회로
+  BackgroundLayer(
+    lines: [r'-+-+-+-||-+-+-+-||-+-+-+-||-+-+-+-||'],
+    scrollSpeed: 0.1,
+    yStart: 0,
+  ),
+  // 데이터 스트림
+  BackgroundLayer(
+    lines: [
+      r' 10110   01101   10110   01101   101',
+      r'    01      10      01      10     ',
+    ],
+    scrollSpeed: 0.2,
+    yStart: 2,
+  ),
+  // 바닥 - 패널
+  BackgroundLayer(
+    lines: [r'[====][====][====][====][====][====]'],
+    scrollSpeed: 0.3,
+    yStart: 7,
+  ),
+];
+
+// ============================================================================
+// 보이드 (Void) - 별/공허
+// ============================================================================
+const _voidLayers = [
+  // 별
+  BackgroundLayer(
+    lines: [r'  *    .    *  .  *    .    *  .  * '],
+    scrollSpeed: 0.03,
+    yStart: 0,
+  ),
+  // 은하
+  BackgroundLayer(
+    lines: [
+      r'     ~*~          ~*~          ~*~  ',
+      r'   *~   ~*      *~   ~*      *~   ~*',
+    ],
+    scrollSpeed: 0.08,
+    yStart: 2,
+  ),
+  // 심연
+  BackgroundLayer(
+    lines: [r'~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.'],
+    scrollSpeed: 0.15,
+    yStart: 7,
+  ),
+];