docs(joinir): Phase 27.10 完了 - ドキュメント更新
- IMPLEMENTATION_LOG.md: Phase 27.10 + 27.10.1 完了記録 - joinir_coverage.md: 責務範囲(D-2)セクション追加 🎉 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
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