maintenance

Cleans up and organizes project files. Use when user mentions '整理', 'cleanup', 'アーカイブ', 'archive', '肥大化', 'Plans.md', 'session-log', or asks to clean up old tasks, archive completed items, or organize files. Do NOT load for: 実装作業, レビュー, 新機能開発, デプロイ.