chore: add .npmrc to disable auto-installing peer dependencies and up… …date package.json build command
2.1.2 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
CI: Node.js 20へ更新、actions/checkout・setup-nodeをv4に更新 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>