kiro universal agent-config format: task-init's hook merge and task-remove's strip break on an upgraded .kiro/agents/*.json (#267) - #270

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/