feat: Add Docker Compose examples

[lowhung]

Summary

Provide ready-to-run Docker Compose examples with message brokers.

Proposed Examples

• docker/rabbitmq: RabbitMQ + buswatch
• docker/kafka: Kafka + Zookeeper + buswatch
• docker/nats: NATS JetStream + buswatch
• docker/full-stack: All brokers + Prometheus + Grafana

Content

• docker-compose.yml files
• Configuration examples
• README with instructions
• Sample producer/consumer scripts

Benefits

• Quick evaluation
• Development environment
• Demo setup