Switch the durable ingestion/maintenance job-dispatch broker decision from
NATS JetStream to RabbitMQ (aio-pika), rewriting ADR-0014 and propagating
the terminology change through ADR-0015, ADR-0016, and the ingestion
vertical-slice plan. Adds aio-pika as a runtime dependency.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>