7b98cca967
Adds the broker-side mechanism for lead-to-lead messages across daemons/hosts (unit 1 of 2): a LeadMessage envelope carrying from/to coord-ids, an AMQP-backed LeadMailbox modeled closely on AmqpReplyInbox (consume-and-hold, deferred manual ack, confirm-mode publish, recovery handling), and a new optional coordinator: config block (separate vhost from broker:, leader traffic only). Config parsing + accessors only — FleetMcp/Fleetd/Injector/ MessageService and the send path are untouched; wiring is a separate ticket.