chore: Assets 디렉토리 구조 정리 및 네이밍 컨벤션 적용

- Assets/_Game/ 하위로 게임 에셋 통합
- External/ 패키지 벤더별 분류 (Synty, Animations, UI)
- 에셋 네이밍 컨벤션 확립 및 적용
  (Data_Skill_, Data_SkillEffect_, Prefab_, Anim_, Model_, BT_ 등)
- pre-commit hook으로 네이밍 컨벤션 자동 검사 추가
- RESTRUCTURE_CHECKLIST.md 작성

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Assets/_Game/Scripts/Skills/Effects/SoundEffect.cs

@@ -0,0 +1,22 @@
+using UnityEngine;
+
+namespace Colosseum.Skills.Effects
+{
+    /// <summary>
+    /// 사운드 재생 효과
+    /// </summary>
+    [CreateAssetMenu(fileName = "SoundEffect", menuName = "Colosseum/Skills/Effects/Sound")]
+    public class SoundEffect : SkillEffect
+    {
+        [Header("Sound Settings")]
+        [SerializeField] private AudioClip clip;
+        [Range(0f, 1f)] [SerializeField] private float volume = 1f;
+
+        protected override void ApplyEffect(GameObject caster, GameObject target)
+        {
+            if (clip == null || caster == null) return;
+
+            AudioSource.PlayClipAtPoint(clip, caster.transform.position, volume);
+        }
+    }
+}