v2.18.0-beta.4 — multi-host updates stay on their host (beta)

Beta thread: #63. Fixes @famewolf's disk-filling remote update: manual batches now route every container to its own host's checker (reproduced end to end against a dind remote, before and after), the pulled-but-inspect-failed ✅ is an honest ❌, and /cleanup walks every managed host. :latest untouched.