docs: Add example applications

[lowhung]

Summary

Create complete example applications demonstrating buswatch usage.

Proposed Examples

• examples/basic-producer-consumer: Simple SDK usage
• examples/rabbitmq-monitoring: RabbitMQ adapter + TUI
• examples/multi-service: Distributed tracing scenario
• examples/prometheus-integration: Prometheus + Grafana setup

Benefits

• Quick start for new users
• Reference implementations
• Integration testing