Counter and histogram metrics were absent from Prometheus scrapes until
the first deployment occurred, making it impossible to distinguish
"no deployments" from "exporter not running" in dashboards and alerts.
Initialize all expected label combinations with zero values when the
collector is created so metrics appear in every scrape from startup.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Add an optional Prometheus metrics HTTP endpoint to the listener for
monitoring deployment operations. Includes four metrics:
- homelab_deploy_deployments_total (counter with status/action/error_code)
- homelab_deploy_deployment_duration_seconds (histogram with action/success)
- homelab_deploy_deployment_in_progress (gauge)
- homelab_deploy_info (gauge with hostname/tier/role/version)
New CLI flags: --metrics-enabled, --metrics-addr (default :9972)
New NixOS options: metrics.enable, metrics.address, metrics.openFirewall
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
