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/Editor/UI/DatabaseUpdateController.cs

@@ -0,0 +1,15 @@
+// Copyright (c) 2024 Synty Studios Limited. All rights reserved.
+//
+// Use of this software is subject to the terms and conditions of the Synty Studios End User Licence Agreement (EULA)
+// available at: https://syntystore.com/pages/end-user-licence-agreement
+//
+// For additional details, see the LICENSE.MD file bundled with this software.
+
+namespace Synty.SidekickCharacters
+{
+    public class DatabaseUpdateController
+    {
+        // This class is no longer required, and will be deleted in the future.
+        // Included as an empty class to remove code dependencies to allow for deletion without causing project errors.
+    }
+}