docs: Add TODO for reusable Checkbox component

추후 재사용 가능한 Checkbox 컴포넌트로 리팩토링 예정:
- 네이티브 checkbox를 숨기고 커스텀 스타일 적용
- 시맨틱 토큰 사용
- MediaAssetFilterMenu, MultiSelect, SingleSelect에서 사용

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: viva-jinyi

src/platform/assets/components/MediaAssetFilterMenu.vue

@@ -1,3 +1,15 @@
+<!--
+TODO: Extract checkbox pattern into reusable Checkbox component
+- Create src/components/input/Checkbox.vue with:
+  - Hidden native <input type="checkbox"> for accessibility
+  - Custom visual styling matching this implementation
+  - Semantic tokens (--primary-background, --input-surface, etc.)
+- Use this Checkbox component in:
+  - MediaAssetFilterMenu.vue (this file)
+  - MultiSelect.vue option template
+  - SingleSelect.vue if needed
+- Benefits: Consistent checkbox UI, better maintainability, reusable design system component
+-->
 <template>
   <div class="flex flex-col gap-0 p-0 m-0">
     <div