🔧 containers: Add persistent volume for RabbitMQ data

Without a named volume, RabbitMQ recreates its Mnesia database on every
container restart, losing queue state and requiring the vhost and user
to be re-provisioned. Adding `rabbitmq_data` as a named volume matches
the pattern already used for PostgreSQL (`pgdata`).

Assisted-by: Claude Opus 4.6 (1M context)
Signed-off-by: Justin Wheeler <jwheel@fedoraproject.org>

podman-compose.yml

@@ -58,6 +58,8 @@ services:
       RABBITMQ_DEFAULT_USER: user
       RABBITMQ_DEFAULT_PASS: pass
       RABBITMQ_DEFAULT_VHOST: vhost
+    volumes:
+      - rabbitmq_data:/var/lib/rabbitmq:z
     healthcheck:
       test: ["CMD", "rabbitmqctl", "status"]
       interval: 10s
@@ -65,3 +67,4 @@ services:
 
 volumes:
   pgdata:
+  rabbitmq_data: