swarmexec v1.6.1 — fix the site deploy trigger

ci:
- deploy-site now sends the downstream infrastruktur/swar-exec-site
  pipeline both IMAGE ($CI_REGISTRY_IMAGE/site) and VERSION as bare semver
  (1.6.1, not the v-prefixed tag), which it requires — the trigger used to
  return HTTP 400 and fail the release's deploy-site job.
- site-image also pushes the bare-semver tag (site:1.6.1) next to :v1.6.1
  and :latest, so the downstream can pull $IMAGE:$VERSION.

No client or agent changes since v1.6.0.