Add public Grafana dashboards for portfolio observability demo

Grafana 11.6 with anonymous read-only access, ClickHouse data source
pointing at SigNoz's store. Pre-provisioned dashboard with 12 panels:
health stats, aggro tick latency percentiles, AI response time, storage
latency, span volume by operation, log volume by severity, recent logs
table, slowest operations, and error spans. Nginx proxy with SSL at
fracture-grafana.georgelarson.me.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: georgeglarson