[AI] 보스 스킬 사용 액션 추가

- UseSkillAction: Behavior Tree에서 스킬 사용을 위한 액션 노드
- Melee_Slash_Boss: 보스 근접 공격 스킬 데이터
- Melee_Slash_Boss_0: 스킬 대미지 효과 (부채꼴 범위)

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

Assets/Scripts/AI/BehaviorActions/Actions/UseSkillAction.cs

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+using System;
+using Colosseum.Skills;
+using Unity.Behavior;
+using UnityEngine;
+using Action = Unity.Behavior.Action;
+using Unity.Properties;
+
+/// <summary>
+/// 지정된 스킬을 사용하는 Behavior Tree Action.
+/// 스킬 실행이 완료될 때까지 Running 상태를 유지합니다.
+/// </summary>
+[Serializable, GeneratePropertyBag]
+[NodeDescription(name: "Use Skill", story: "[스킬] 사용", category: "Action", id: "799f1e8cfafa78b2d52ef61a6bbb29b9")]
+public partial class UseSkillAction : Action
+{
+    [SerializeReference] public BlackboardVariable<SkillData> 스킬;
+
+    private SkillController skillController;
+
+    protected override Status OnStart()
+    {
+        // 스킬 데이터 확인
+        if (스킬?.Value == null)
+        {
+            Debug.LogWarning("[UseSkillAction] 스킬이 null입니다.");
+            return Status.Failure;
+        }
+
+        // SkillController 컴포넌트 가져오기
+        skillController = GameObject.GetComponent<SkillController>();
+        if (skillController == null)
+        {
+            Debug.LogWarning($"[UseSkillAction] SkillController를 찾을 수 없습니다: {GameObject.name}");
+            return Status.Failure;
+        }
+
+        // 스킬 실행 시도
+        bool success = skillController.ExecuteSkill(스킬.Value);
+        if (!success)
+        {
+            // 이미 다른 스킬 사용 중이거나 쿨타임
+            return Status.Failure;
+        }
+
+        return Status.Running;
+    }
+
+    protected override Status OnUpdate()
+    {
+        // SkillController가 해제된 경우
+        if (skillController == null)
+        {
+            return Status.Failure;
+        }
+
+        // 스킬 애니메이션이 종료되면 성공
+        if (!skillController.IsPlayingAnimation)
+        {
+            return Status.Success;
+        }
+
+        return Status.Running;
+    }
+
+    protected override void OnEnd()
+    {
+        skillController = null;
+    }
+}

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