feat: implement Grafana for observability and monitoring

## Summary

Add Grafana dashboards for monitoring the CNG Sandbox stack.

## Motivation

Provide visibility into service health, ingestion pipeline performance, and resource utilization across the Docker stack.

## Scope (TBD)

- Metrics collection (Prometheus or similar) from ingestion API, tilers, and database
- Grafana dashboard for key metrics (job queue depth, conversion times, error rates, container resource usage)
- Alert rules for service degradation
- Integration with existing Docker Compose setup

## Reference

https://grafana.com/