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/Database/DTO/SidekickDBVersion.cs

@@ -0,0 +1,39 @@
+// 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.
+
+using SQLite;
+using System;
+
+namespace Synty.SidekickCharacters.Database.DTO
+{
+    [Table("sk_vdata")]
+    public class SidekickDBVersion
+    {
+        [PrimaryKey, AutoIncrement, Column("id")]
+        public int ID { get; set; }
+        [Column("semantic_version")]
+        public string SemanticVersion { get; set; }
+        [Column("update_time")]
+        public DateTime LastUpdated { get; set; }
+
+        /// <summary>
+        ///     Updates or Inserts this item in the Database.
+        /// </summary>
+        /// <param name="dbManager">The database manager to use.</param>
+        public int Save(DatabaseManager dbManager)
+        {
+            if (ID <= 0)
+            {
+                dbManager.GetCurrentDbConnection().Insert(this);
+                // in theory this could return a different ID, but in practice it's highly unlikely
+                ID = (int) SQLite3.LastInsertRowid(dbManager.GetCurrentDbConnection().Handle);
+            }
+            dbManager.GetCurrentDbConnection().Update(this);
+            return ID;
+        }
+    }
+}