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>

README.md

@@ -91,6 +91,12 @@ error: www.adbraun.lol has a CNAME, so it can't have any other records (found A)
 * **Let's Encrypt DNS-01** built in: `jarl acme` plus certbot, acme.sh and lego
   hooks, an HTTPS-only endpoint for lego's and Traefik's `httpreq` provider,
   and CNAME delegation to a dedicated ACME zone.
+* **Certificates for the server itself**: Jarl obtains and renews TLS
+  certificates from Let's Encrypt (or any ACME CA), answering the DNS-01
+  challenge in its own zones or through Porkbun's API while Porkbun still
+  serves the domain, decided at every renewal. Use them for the web UI
+  (HTTPS without a restart) and for named's DNS over TLS and HTTPS (named
+  rereads them on renewal), or bring your own.
 * **Adopts an existing server**: imports named.conf and zone files
   (comments included), then switches named over with an automatic
   fallback.
@@ -132,6 +138,7 @@ in `/etc/jarl/jarl.yaml` to reach it from your management network.
 | [docs/views.md](docs/views.md) | Split DNS: adding views to a server that has none |
 | [docs/dnssec.md](docs/dnssec.md) | DNSSEC signing, going public with your own name servers, Porkbun |
 | [docs/acme.md](docs/acme.md) | Let's Encrypt DNS-01 with certbot, acme.sh, lego and Traefik |
+| [docs/certificates.md](docs/certificates.md) | TLS certificates Jarl obtains and renews for its web UI and named's DNS over TLS/HTTPS |
 | [docs/stats.md](docs/stats.md) | Query statistics: enabling, what is collected, retention |
 | [docs/exposure.md](docs/exposure.md) | Internet exposure: which views are public, hardening checks, response rate limiting |
 | [docs/metrics.md](docs/metrics.md) | Prometheus metrics: access, what is exported, example alerts |