Add admin/docs/offline-install.md covering the build-and-carry workflow,
bundle layout and manifest, how artifact mode stays offline, GPU support,
bundling Supply Depot apps, updating an air-gapped install, troubleshooting,
and an explicit statement of what is and is not covered.
Link it from the README and soften the two "stable internet connection
required during install" lines to point at it.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Ken Eucker