Publishes backoffice.*Maintenance.*; null publishes nothing (tests).
Global kill-switch state. Distinct from any service's own flag — a service
reports on: false from listServices while global is on, because
that field is its per-service flag. Effective state is the OR of the two.
Flips the global kill-switch, gating every process that runs the gate — including services that never registered, which no per-service toggle can reach. The control plane (this dashboard) is exempt by construction.
Admin-side maintenance toggle over the Valkey-only MaintenanceService.