Harden explorer Docker Compose resource controls

[numbers-official]

Summary

• Add Docker Compose memory/swap limits for backend, DB, stats, stats DB, and Redis
• Add backend healthcheck for indexing-status endpoint
• Add Docker json-file log rotation defaults for high-volume services
• Document production hardening steps for monitoring and process metrics

Verification

• Parsed all docker-compose YAML files with PyYAML
• Production mainnet explorer remained healthy after applying runtime memory limits: homepage and indexing-status endpoint returned HTTP 200

Notes

• No production secrets were added. Limit values are configurable via environment variables.