feat(animation): Act 기반 몬스터 사이즈 시스템 추가

- Act 진행에 따른 몬스터 사이즈 확률 조정
- 보스: Act별 고정 사이즈 (소/중/대)
- 일반/엘리트: Act별 확률 랜덤
- TaskInfo에 monsterSize 필드 추가
- 애니메이션 패널에서 Act 기반 사이즈 사용

lib/src/core/animation/monster_size.dart

@@ -1,5 +1,8 @@
 // 몬스터 크기 시스템
-// 몬스터 레벨에 따라 ASCII 아트 크기 결정
+// Act와 몬스터 등급에 따라 ASCII 아트 크기 결정
+
+import 'package:asciineverdie/src/core/model/monster_grade.dart';
+import 'package:asciineverdie/src/core/util/deterministic_random.dart';
 
 /// 몬스터 크기 enum
 /// 실제 프레임 줄 수와 일치하도록 설정
@@ -48,3 +51,55 @@ MonsterSize getMonsterSize(int? level) {
 int getMonsterVerticalPadding(MonsterSize size) {
   return (7 - size.lines) ~/ 2;
 }
+
+// =============================================================================
+// Act 기반 몬스터 사이즈 결정 (Phase 13)
+// =============================================================================
+
+/// 보스 몬스터 사이즈 결정 (Act별 고정)
+///
+/// - Prologue(1), Act I(2): small (4줄)
+/// - Act II(3), Act III(4): medium (6줄)
+/// - Act IV(5), Act V(6)+: large (8줄)
+MonsterSize getBossSizeForAct(int plotStageCount) {
+  if (plotStageCount <= 2) return MonsterSize.small;
+  if (plotStageCount <= 4) return MonsterSize.medium;
+  return MonsterSize.large;
+}
+
+/// 일반/엘리트 몬스터 사이즈 결정 (Act별 확률 랜덤)
+///
+/// Act가 진행될수록 큰 몬스터가 나올 확률 증가.
+/// 프롤로그에서는 대형 몬스터 0%.
+MonsterSize getRandomSizeForAct(int plotStageCount, DeterministicRandom rng) {
+  final roll = rng.nextInt(100);
+
+  // Act별 확률 테이블 (small %, medium %, large = 나머지)
+  final (smallChance, mediumChance) = switch (plotStageCount) {
+    <= 1 => (70, 30), // Prologue: 70% small, 30% medium, 0% large
+    2 => (50, 40), // Act I: 50% small, 40% medium, 10% large
+    3 => (35, 40), // Act II: 35% small, 40% medium, 25% large
+    4 => (25, 40), // Act III: 25% small, 40% medium, 35% large
+    5 => (15, 35), // Act IV: 15% small, 35% medium, 50% large
+    _ => (10, 25), // Act V+: 10% small, 25% medium, 65% large
+  };
+
+  if (roll < smallChance) return MonsterSize.small;
+  if (roll < smallChance + mediumChance) return MonsterSize.medium;
+  return MonsterSize.large;
+}
+
+/// 몬스터 등급과 Act에 따른 사이즈 결정 (통합 함수)
+///
+/// 보스: Act별 고정 사이즈
+/// 일반/엘리트: Act별 확률 랜덤
+MonsterSize getMonsterSizeForAct({
+  required int plotStageCount,
+  required MonsterGrade grade,
+  required DeterministicRandom rng,
+}) {
+  if (grade == MonsterGrade.boss) {
+    return getBossSizeForAct(plotStageCount);
+  }
+  return getRandomSizeForAct(plotStageCount, rng);
+}

lib/src/core/engine/act_progression_service.dart

@@ -1,6 +1,7 @@
 import 'dart:math' as math;
 
 import 'package:asciineverdie/data/game_text_l10n.dart' as l10n;
+import 'package:asciineverdie/src/core/animation/monster_size.dart';
 import 'package:asciineverdie/src/core/engine/combat_calculator.dart';
 import 'package:asciineverdie/src/core/model/combat_state.dart';
 import 'package:asciineverdie/src/core/model/combat_stats.dart';
@@ -253,6 +254,7 @@ class ActProgressionService {
         monsterPart: '*', // 특수 전리품
         monsterLevel: glitchGod.level,
         monsterGrade: MonsterGrade.boss, // 최종 보스는 항상 boss 등급
+        monsterSize: MonsterSize.large, // 최종 보스는 항상 대형
       ),
       currentCombat: combatState,
     );

lib/src/core/engine/progress_service.dart

@@ -1,6 +1,7 @@
 import 'dart:math' as math;
 
 import 'package:asciineverdie/data/game_text_l10n.dart' as l10n;
+import 'package:asciineverdie/src/core/animation/monster_size.dart';
 import 'package:asciineverdie/src/core/engine/act_progression_service.dart';
 import 'package:asciineverdie/src/core/engine/combat_calculator.dart';
 import 'package:asciineverdie/src/core/engine/combat_tick_service.dart';
@@ -585,6 +586,7 @@ class ProgressService {
           monsterPart: '*', // Boss는 WinItem 드랍
           monsterLevel: actBoss.monsterStats.level,
           monsterGrade: MonsterGrade.boss,
+          monsterSize: getBossSizeForAct(state.progress.plotStageCount),
         ),
         currentCombat: actBoss,
       );
@@ -673,6 +675,13 @@ class ProgressService {
       durationMillis,
     );
 
+    // 몬스터 사이즈 결정 (Act 기반, Phase 13)
+    final monsterSize = getMonsterSizeForAct(
+      plotStageCount: state.progress.plotStageCount,
+      grade: monsterResult.grade,
+      rng: state.rng,
+    );
+
     progress = taskResult.progress.copyWith(
       currentTask: TaskInfo(
         caption: taskResult.caption,
@@ -681,6 +690,7 @@ class ProgressService {
         monsterPart: monsterResult.part,
         monsterLevel: effectiveMonsterLevel,
         monsterGrade: monsterResult.grade,
+        monsterSize: monsterSize,
       ),
       currentCombat: combatState,
     );

lib/src/core/model/game_state.dart

@@ -1,5 +1,6 @@
 import 'dart:collection';
 
+import 'package:asciineverdie/src/core/animation/monster_size.dart';
 import 'package:asciineverdie/src/core/model/combat_event.dart';
 import 'package:asciineverdie/src/core/model/combat_state.dart';
 import 'package:asciineverdie/src/core/model/equipment_item.dart';
@@ -315,6 +316,7 @@ class TaskInfo {
     this.monsterPart,
     this.monsterLevel,
     this.monsterGrade,
+    this.monsterSize,
   });
 
   final String caption;
@@ -326,12 +328,15 @@ class TaskInfo {
   /// 킬 태스크의 전리품 부위 (예: "claw", "tail", "*"는 WinItem)
   final String? monsterPart;
 
-  /// 킬 태스크의 몬스터 레벨 (애니메이션 크기 결정용)
+  /// 킬 태스크의 몬스터 레벨 (전투 스탯 계산용)
   final int? monsterLevel;
 
   /// 킬 태스크의 몬스터 등급 (Normal/Elite/Boss)
   final MonsterGrade? monsterGrade;
 
+  /// 킬 태스크의 몬스터 사이즈 (애니메이션 크기 결정용, Act 기반)
+  final MonsterSize? monsterSize;
+
   factory TaskInfo.empty() =>
       const TaskInfo(caption: '', type: TaskType.neutral);
 
@@ -342,6 +347,7 @@ class TaskInfo {
     String? monsterPart,
     int? monsterLevel,
     MonsterGrade? monsterGrade,
+    MonsterSize? monsterSize,
   }) {
     return TaskInfo(
       caption: caption ?? this.caption,
@@ -350,6 +356,7 @@ class TaskInfo {
       monsterPart: monsterPart ?? this.monsterPart,
       monsterLevel: monsterLevel ?? this.monsterLevel,
       monsterGrade: monsterGrade ?? this.monsterGrade,
+      monsterSize: monsterSize ?? this.monsterSize,
     );
   }
 }