Certificates for other hosts: jarl cert get

jarld obtains and renews a certificate for another host; the host asks
for it with one command, waits, downloads it when it is newer than its
copy and runs a hook with the paths in JARL_CERT_* variables.

- Certificates have an owner user; another user can't take the name.
  An existing one is obtained again only when a name is added or
  removed. A new certificates grant (names=) says which names a user
  may have; it is never part of "*". Users may own
  certificates.max_per_user certificates (10) or their own cert_limit.
- POST /certificates/{name}/request; owners may list, show, export and
  delete theirs; keys only over HTTPS, the socket or loopback; every
  download is recorded and shown as "Pulled by".
- CLI: jarl cert get (saved settings, all saved when no name), cert
  saved, cert forget, cert schedule (daily systemd timer, Linux, root).
- Migration 14. Tests: server, auth, and e2e against Pebble.

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

docs/permissions.md

@@ -118,7 +118,8 @@ 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, use the registrar (Porkbun,
 whose key can move the domain), and manage TLS certificates (whose keys
-can impersonate the server; [certificates.md](certificates.md)).
+can impersonate the server; [certificates.md](certificates.md)). The one
+exception is certificates for other hosts, below.
 
 A grant is written as:
 
@@ -137,7 +138,8 @@ RESOURCE:ACCESS [zones=PATTERNS] [views=PATTERNS] [names=PATTERNS] [types=TYPES]
 | `audit` | everyone's audit events and changesets (without it, users see only their own) |
 | `stats` | query statistics, including client addresses and the names they look up (read only) |
 | `blocking` | blocklists and block/allow rules ([blocking.md](blocking.md)); `write` also downloads lists now |
-| `*` | all of the above |
+| `certificates` | certificates for other hosts (`jarl cert get`), by the names in them: `write` gets one obtained, `read` only downloads it. Never part of `*` |
+| `*` | all of the above, except `certificates` |
 
 `ACCESS` is `read` or `write` (write includes read). Filters narrow a grant.
 Each takes comma separated patterns where `*` and `?` are wildcards, and a
@@ -146,6 +148,8 @@ missing filter matches everything:
 * `zones=adbraun.lol,*.adbraun.lol`: zone names, without the final dot
 * `views=internal`: view names (`_default` means zones outside any view)
 * `names=_acme-challenge.*`: record owner names, as FQDNs without the final dot
+  (for `certificates`: the names in the certificate; `*.adbraun.lol` also
+  allows the wildcard certificate `*.adbraun.lol`)
 * `types=TXT,CNAME`: record types
 
 Examples:
@@ -157,6 +161,7 @@ zones:write zones=*.lab.adbraun.lol                       create/delete zones be
 records:write zones=adbraun.lol views=internal            only the internal copy of a split zone
 records:write names=_acme-challenge.* types=TXT           ACME challenges anywhere
 records:write zones=acme.adbraun.lol types=TXT            only TXT records in a dedicated ACME zone
+certificates:write names=mail.adbraun.lol,smtp.adbraun.lol certificates for a mail server (jarl cert get)
 ```
 
 A user who may see some records of a zone may also see that the zone exists