stage0 netboot rework, mkuki library, and local full-chain test harness - #8

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/upload-artifact@330a01c490aca151604b8cf639adc76d48f6c5d4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/