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>

docs/permissions.md

@@ -116,8 +116,9 @@ demote or delete the last enabled administrator.
 
 A user's permissions are a list of grants. Administrators (`admin: true`)
 may do everything, and only they can manage users, see everyone's tokens,
-run `resync`, wipe a zone's DNSSEC keys, and use the registrar (Porkbun,
-whose key can move the domain).
+run `resync`, wipe a zone's DNSSEC keys, use the registrar (Porkbun,
+whose key can move the domain), and manage TLS certificates (whose keys
+can impersonate the server; [certificates.md](certificates.md)).
 
 A grant is written as: