enhance(frontend): MkPostFormSimpleもファイルアップロードのファイル選択を従来のものに変更

[4ster1sk]

What

Why

Additional info (optional)

Checklist

• コントリビューションガイドを読みました( Read the contribution guide)
• ローカル環境で動作しました(Test working in a local environment)
• (必要なら)CHANGELOG_YOJO.mdの更新((If needed) Update CHANGELOG_YOJO.md)
• (必要なら)テストの追加((If possible) Add tests)

[codecov]

Codecov Report

❌ Patch coverage is 0% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 19.12%. Comparing base (e70f293) to head (1624c22).

Files with missing lines	Patch %	Lines
...kages/frontend/src/components/MkPostFormSimple.vue	0.00%	20 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           develop    #1058       +/-   ##
============================================
- Coverage    39.65%   19.12%   -20.54%     
============================================
  Files         1942      959      -983     
  Lines       217409    97871   -119538     
  Branches      3402     1434     -1968     
============================================
- Hits         86222    18717    -67505     
+ Misses      131120    79147    -51973     
+ Partials        67        7       -60     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[kozakura913]

#1050 の考慮漏れ