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/Resources/Styles/EditorStyles.uss

@@ -0,0 +1,25 @@
+.colorSelectionRow
+{
+    flex-direction: row;
+    width: 100%;
+    align-content: flex-start;
+    align-items: flex-start;
+    flex-wrap: wrap;
+}
+
+.colorSelectionRowContent
+{
+    flex-direction: row;
+    max-width: 80%;
+    align-content: flex-start;
+    align-items: flex-start;
+    flex-wrap: wrap;
+    /* TODO: Uncomment once all colors options are re-enabled */
+    /*justify-content: space-between;*/
+}
+
+.colorSelectionRowLabel
+{
+    min-width: 150px;
+    max-width: 20%;
+}