Builds Hugo and writes the output to /srv/www/blog on push to main.
Runs in a node:20-bookworm container with /srv/www bind-mounted from
the shinobi host (allowed via the gitea-runner's valid_volumes config).
Caddy on the host serves /srv/www/blog directly.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
