Adds full ELK stack as a Docker Compose overlay for powerful trace_id-based log search:

- Elasticsearch 8.13: single-node, daily index rotation, 30-day ILM retention
- Logstash: parses structured JSON logs, extracts trace_id/request_id/user_id as keyword fields
- Kibana: pre-configured index pattern (meridian-logs-*) + saved searches (Trace Lookup, Error Explorer)
- Filebeat: tails Docker container logs with metadata enrichment
- Auto-setup: kibana-setup sidecar imports saved objects on first boot

Usage: docker compose -f docker-compose.yml -f docker-compose.elk.yml up
Trace search: Kibana → Discover → trace_id:"<your-X-Trace-ID>"

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>