Switch all ACME certificate issuance from step-ca (ca.home.2rjus.net)
to OpenBao PKI (vault.home.2rjus.net:8200/v1/pki_int/acme/directory).
- Update default ACME server in system/acme.nix
- Update Caddy acme_ca in http-proxy and nix-cache services
- Remove labmon service from monitoring01 (step-ca monitoring)
- Remove labmon scrape target and certificate_rules alerts
- Remove alloy.nix (only used for labmon profiling)
- Add docs/plans/cert-monitoring.md for future cert monitoring needs
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
