refactor(frontend): use deepClone

[kakkokari-gtyih]

What

JSON.parse(JSON.stringify()) は遅いため（deepClone で Vue のプロキシも解除される）

Why

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

[codecov]

Codecov Report

❌ Patch coverage is 10.00000% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 17.68%. Comparing base (e98252a) to head (8f10827).
⚠️ Report is 1339 commits behind head on develop.

Files with missing lines	Patch %	Lines
packages/frontend/src/composables/use-form.ts	0.00%	8 Missing ⚠️
packages/frontend/src/accounts.ts	25.00%	3 Missing ⚠️
...ckages/frontend/src/pages/drop-and-fusion.game.vue	0.00%	3 Missing ⚠️
...c/pages/admin/custom-emojis-manager.local.list.vue	0.00%	2 Missing ⚠️
packages/frontend/src/preferences/manager.ts	33.33%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           develop   #16305       +/-   ##
============================================
- Coverage    42.56%   17.68%   -24.89%     
============================================
  Files         1685      860      -825     
  Lines       170650    78759    -91891     
  Branches      4223     1335     -2888     
============================================
- Hits         72643    13931    -58712     
+ Misses       97546    64822    -32724     
+ Partials       461        6      -455     

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[kakkokari-gtyih]

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