agent/ becomes the repository root, so the module is
gitea.hostxtra.co.uk/vantage/vantage-agent, and installer/ comes with it.
Releases move to this repository, and internal/sync's self-update URLs
move with them. Agents built before this point have the old
mrhid6/vantage path compiled in and will fail the push-button update;
re-running the server-generated /update one-liner on each host moves
them onto a build that knows the new address.
