Configure Grafana Unified Alerting with file-based provisioned alert rules, contact points, and notification policies. Add stable UID to Loki datasource for alert rule references. Update LOGGING.md with dashboard descriptions, alerting rules table, and LogQL query reference. Alert rules: Error Rate Spike (critical), Container Silence for backend/postgres/redis (warning), 5xx Response Spike (critical). Co-Authored-By: Claude Opus 4.6 <[email protected]>