Prometheus metrics collector correlating StepFlow's expected LIVE direct_messaging queues with their RabbitMQ lifecycle (MINT-8250).

StepFlow (this collector) exposes what is expected: the queue of every active (not yet terminated) LIVE worker. The RabbitMQ exporter exposes what is observed (rabbitmq_queue_messages_ready, rabbitmq_queue_consumers, ...). Correlating the two in PromQL flags a direct_messaging_* queue present in RabbitMQ but absent here as a candidate orphan, without duplicating the read-only correlation already done in the worker-manager live_state module (MINT-8249).