enhance(frontend): アイコンデコレーション管理画面にプレビューを追加

[kakkokari-gtyih]

What

Why

Fix #14490

Additional info (optional)

Checklist

• Read the contribution guide
• Test working in a local environment
• (If needed) Add story of storybook
• (If needed) Update CHANGELOG.md
• (If possible) Add tests

[syuilo]

展開の操作なしにプレビューが表示されているUIがよさそう

[kakkokari-gtyih]

展開の操作なしにプレビューが表示されているUIがよさそう

MkFolderが使えなくなるので結構大規模な変更になるかも（プレビューが出るようにするのを優先するならとりあえずこれで行って後からさらに改修するのも手）

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 80 lines in your changes missing coverage. Please review.

Project coverage is 20.16%. Comparing base (3fe7e37) to head (8d21534).
Report is 4 commits behind head on develop.

Files with missing lines	Patch %	Lines
packages/frontend/src/pages/avatar-decorations.vue	0.00%	80 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #14511      +/-   ##
===========================================
- Coverage    20.17%   20.16%   -0.02%     
===========================================
  Files          725      725              
  Lines       100502   100569      +67     
  Branches      1045     1045              
===========================================
  Hits         20279    20279              
- Misses       79681    79748      +67     
  Partials       542      542              

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[syuilo]

👍🏻