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>

internal/server/routes.go

@@ -175,6 +175,7 @@ func (s *Server) routes() {
 	m.HandleFunc("POST "+p+"/certificates/check", s.authed(s.certCheck))
 	m.HandleFunc("GET "+p+"/certificates/{name}", s.authed(s.certGet))
 	m.HandleFunc("GET "+p+"/certificates/{name}/pem", s.authed(s.certPEM))
+	m.HandleFunc("POST "+p+"/certificates/{name}/request", s.authed(s.certRequest))
 	m.HandleFunc("PATCH "+p+"/certificates/{name}", s.authed(s.certUpdate))
 	m.HandleFunc("DELETE "+p+"/certificates/{name}", s.authed(s.certDelete))
 	m.HandleFunc("POST "+p+"/certificates/{name}/issue", s.authed(s.certIssue))