Enable k3s single-node server on ringtail (NixOS) for native amd64
container builds. Includes ArgoCD Application and manifests for a
Forgejo Actions runner with the `k8s-amd64` label, Ansible bootstrap
tasks for k3s token and runner secret, and containerd registry mirrors
pulling through Zot on indri.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
