Add a build-and-deploy pipeline

The pipeline should prove the artifact is valid, ship an immutable image tag, and check the live route before it reports success.

Flow

Build the image from the static site tree.
Run a content validation step.
Push a SHA tag and optionally `latest`.
Roll the Kubernetes deployment or patch the image reference.
Verify the URL returns 200.

Example workflow snippet

docker build -t ghcr.io/your-org/site:${GITHUB_SHA} webpages
docker push ghcr.io/your-org/site:${GITHUB_SHA}
ssh "${DEPLOY_USER}@${DEPLOY_HOST}" \
  "k3s kubectl -n k8s-oci rollout status deployment/webpages --timeout=120s"
curl -fsS https://rghf.nl