Add workflow_dispatch for manual release from Actions UI

[39ff]

• Add workflow_dispatch trigger with optional release_tag input
• Release job runs on tag push OR manual dispatch with tag specified
• tag_name is set from input or ref_name for consistent behavior

[coderabbitai]

Walkthrough

GitHub Actions のビルドワークフローに手動実行（workflow_dispatch と release_tag 入力）を追加し、リリースジョブの実行条件を拡張。GitHub Release の tag_name を入力 release_tag または現在の ref 名に設定するよう変更。

Changes

Cohort / File(s)	Summary
CI Workflow .github/workflows/build.yml	workflow_dispatch に release_tag 入力を追加。リリースジョブ条件を「refs/tags/v* または 手動実行で release_tag 指定」に拡張。Release ステップの tag_name を release_tag 優先、未指定時は github.ref に設定。

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

ぽん、とタグが跳ねた夜
にんじん色の月、release_tag を抱えて
ぼくはボタンをちょいと押す
refs/tags/v の道も、手動の道も
風に揺れる YAML の草むらで
ぴょんぴょん、版の名を刻む 🥕

---

Note

🎁 Summarized by CodeRabbit Free

Your organization is on the Free plan. CodeRabbit will generate a high-level summary and a walkthrough for each pull request. For a comprehensive line-by-line review, please upgrade your subscription to CodeRabbit Pro by visiting https://app.coderabbit.ai/login.

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