Self-hosted respellion-linux runner not required — Gitea's hosted
ubuntu-latest runner has Docker + Compose v2 out of the box, so
make smoke works without any manual registration step.
Updates docs/runbooks/ci.md to reflect the new runner label and
removes the act_runner self-hosted setup as the primary path.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
