feat: consume transactional email notifications

Add contract validation, SMTP delivery results, terminal failure context, neutral development seeding, and local Docker setup.

Ref: IT-1033

docker/environments/docker-compose.yml

@@ -40,6 +40,7 @@ services:
       - App__RabbitMq__Port=5672
       - App__RabbitMq__User=${RABBITMQ_USER:?RABBITMQ_USER is required}
       - App__RabbitMq__Password=${RABBITMQ_PASSWORD:?RABBITMQ_PASSWORD is required}
+      - App__RabbitMq__VirtualHost=${RABBITMQ_VIRTUAL_HOST:-/}
     depends_on:
       db:
         condition: service_healthy
@@ -92,4 +93,4 @@ volumes:
 
 networks:
   internal:
-    driver: bridge
+    driver: bridge