ci: remove obsolete GitHub workflows

[Yusuke4869]

GitHub App (flightdesk/preflight) 導入により不要になった workflow を削除

Summary by CodeRabbit

• 変更
  • プルリクエスト作成者を自動で担当者に割り当てる機能を削除しました。
  • プルリクエストのタイトルを自動検証し、結果をコメントで通知する機能を削除しました。

[coderabbitai]

Navigate logical layers of code changes, visualize relationships, and explore their blast radius.

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Advanced

Run ID: b898f828-5422-428e-979e-6e1c63b42f63

📥 Commits

Reviewing files that changed from the base of the PR and between c02841f and 4199428.

📒 Files selected for processing (2)

• .github/workflows/auto-author-assign.yml
• .github/workflows/semantic-pr-title.yml

💤 Files with no reviewable changes (2)

• .github/workflows/semantic-pr-title.yml
• .github/workflows/auto-author-assign.yml

Included review availability: Your plan provides up to 1 included review per hour; 0 remain after this review.

📜 Recent review details

⏰ Context from checks skipped due to timeout. (2)

• GitHub Check: CI
• GitHub Check: Validate PR title

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📝 Walkthrough

Walkthrough

作成者を担当者に割り当てるワークフローと、PRタイトルを検証してコメントを管理するワークフローを削除しました。

Changes

作成者の自動割り当て

Layer / File(s)	Summary
自動割り当てワークフローの削除 .github/workflows/auto-author-assign.yml	PR作成時と再オープン時に作成者を担当者に割り当てるワークフローと、書き込み権限設定を削除しました。

PRタイトル検証

Layer / File(s)	Summary
タイトル検証ワークフローの削除 .github/workflows/semantic-pr-title.yml	PRタイトルの検証、失敗時の説明コメント投稿、成功時の既存コメント削除を行うワークフローを削除しました。

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~8 minutes

Change: Other

Merge Risk: ⚪ Minimal · up to 41994

The workflows have been removed as intended. No concrete issue is established that prevents merging.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	PR タイトルは、不要になった GitHub Actions ワークフローの削除という主な変更を正確に要約しています。簡潔で具体的です。
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Commit to this branch
• Create a new PR

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_{うさぎは差分をぴょんと読み
二つの手順が静かに消える
作成者を割り当てる仕組み
タイトルを確かめる仕組み
月明かりの下、草をかじる
新しい朝へ耳を立てる}

_{Comment @coderabbitai help to get the list of available commands.}