Drop k8s-server from flake, Makefile targets, modules
(kubernetes.nix, docker-registry.nix), install script and
hardware config. Remove related registry vhost, port 6443
and NAT rules from gateway.nix. Drop K8s-Server section
and dangling markdown wrapper from README.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>