TLS certificates: Jarl obtains and renews them over ACME

Jarl is now an ACME client (lego's core, no DNS providers). It answers
DNS-01 challenges in a zone it serves, or through Porkbun's DNS API while
Porkbun serves the domain; "auto" decides from the domain's public name
servers at every renewal, and a CNAME on _acme-challenge is followed.
Certificates are used for jarld's HTTPS (served without a restart; each
port speaks HTTPS and plain HTTP, plain HTTP from loopback and trusted
proxies still served) and/or written for named's DNS over TLS/HTTPS, with
rndc reconfig on renewal. Renewal follows the CA's ARI window or two
thirds of the lifetime, with back-off. Certificates you renew yourself
can be used too. Certificates page and dashboard card, jarl cert,
/api/v1/certificates, Prometheus gauges, docs/certificates.md, and an
e2e section against Pebble.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/server/h_changes.go

@@ -283,6 +283,7 @@ func (s *Server) status(w http.ResponseWriter, r *http.Request, p *auth.Principa
 	if p.IsAdmin() {
 		resp.Backup = s.backupStatus(r.Context(), now)
 		resp.TOTP = s.totpOverview(r.Context())
+		resp.Certificates = s.certSummary(r.Context())
 	}
 	if p.Can(auth.Action{Resource: auth.ResBlocking}) {
 		resp.BlocklistErrors = s.blocklistErrors(r.Context())