agent/ becomes the root of gitea.hostxtra.co.uk/vantage/vantage-agent,
with installer/ alongside it, and agent-release.yml goes with them.
Releases now come from that repository, so the six places this server
generates or reads a release URL are repointed: both install scripts,
both update scripts, and the latest-version lookup in dispatch.go. The
agent/v* tag prefix is unchanged — those scripts grep for it.
Agents built before this move have the old mrhid6/vantage path compiled
into their self-update and will 404 on the push-button update. The
remedy is the /update one-liner, which this server generates and which
therefore has to ship first.