Configurable queue names

### Description

The names of the RabbitMQ queues used by the frontier and worker should be configurable via environmental variables.

Start at the frontier and worker entry points where RabbitMQ queues are declared or consumed, then trace how their names are currently supplied. Add environmental-variable configuration for both queue names and verify that each component uses the configured values. No files or tests are named in the issue, so first locate the RabbitMQ setup and existing configuration conventions.

Written by the indexing model from the issue text.