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

• [x] Read the contribution guide
• [ ] Test working in a local environment
• [ ] (If needed) Add story of storybook
• [x] (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[bot]]

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 :warning:

Additional details and impacted files

```diff @@ 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]

👍🏻