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/External/Models/SidekickCharacters/Scripts/Runtime/Utils/PartUtils.cs

@@ -0,0 +1,24 @@
+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+
+namespace Synty.SidekickCharacters.Utils
+{
+    public static class PartUtils
+    {
+        /// <summary>
+        ///     Checks if a given part is a base part or not.
+        /// </summary>
+        /// <param name="partName">The name of the part to check.</param>
+        /// <returns>true if it is a base part; otherwise false</returns>
+        public static bool IsBaseSpeciesPart(string partName)
+        {
+            if (string.IsNullOrEmpty(partName))
+            {
+                return false;
+            }
+
+            return partName.Contains("_BASE_");
+        }
+    }
+}