enhance(frontend): フォロワーへのメッセージ欄を改良

[kakkokari-gtyih]

What

• 吹き出しにする
• 「フォロワーへのメッセージ」であることを明記する

Why

今のままだと何らかの警告表示に見間違えそうなので

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

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 99.14530% with 1 line in your changes missing coverage. Please review.

Project coverage is 19.52%. Comparing base (a3d236c) to head (e35bc20). Report is 204 commits behind head on develop.

Files with missing lines	Patch %	Lines
packages/frontend/src/components/MkFukidashi.vue	99.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #14656 +/- ## ============================================ - Coverage 41.74% 19.52% -22.23% ============================================ Files 1549 716 -833 Lines 196555 101490 -95065 Branches 2767 987 -1780 ============================================ - Hits 82055 19815 -62240 + Misses 113939 81129 -32810 + Partials 561 546 -15 ```

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[syuilo]

🙏🏻