Joins NodeTag (key='role') to the node last seen Prometheus metric so
alert rules can target infrastructure nodes only (role="infra").
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Add /metrics endpoint with Prometheus gauges for nodes, messages,
advertisements, telemetry, trace paths, events, and members. Include
per-node last_seen timestamps for alerting. Add Alertmanager service
to Docker Compose metrics profile with default blackhole receiver.
Add NodeNotSeen alert rule (48h threshold). Add 1h time window to
all windowed metrics alongside existing 24h/7d/30d windows.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>