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/web/static/assets/pages/users.js

@@ -54,6 +54,7 @@ async function userDialog(u, grants) {
     tmpl.value = "";
   });
   const comment = input({ value: u ? u.comment : "" });
+  const certLimit = input({ type: "number", min: "0", value: u && u.cert_limit != null ? String(u.cert_limit) : "", placeholder: "certificates.max_per_user" });
   await modal(u ? "Edit " + u.username : "New user", h("div", null, h("div", { class: "form-grid" },
     field("Username", name),
     field("Password", pw),
@@ -62,6 +63,7 @@ async function userDialog(u, grants) {
     u ? h("span") : null, u ? disabled : null,
     field("Permissions", gr, "One grant per line (ignored for administrators)."),
     h("span"), tmpl,
+    field("Certificates", certLimit, "How many certificates this user may own through jarl cert get (needs a certificates grant). Empty: the default from jarl.yaml."),
     field("Comment", comment)), err), [
     { label: "Cancel", value: null },
     { label: u ? "Save" : "Create user", kind: "primary", onclick: async () => {
@@ -69,6 +71,8 @@ async function userDialog(u, grants) {
       if (service.input.checked) data.password = "";
       else if (pw.value) data.password = pw.value;
       if (u) data.disabled = disabled.input.checked;
+      if (certLimit.value.trim() !== "") data.cert_limit = Number(certLimit.value);
+      else if (u && u.cert_limit != null) data.cert_limit = -1;
       try {
         if (u) await api("PATCH", "/users/" + u.id, { body: data });
         else await api("POST", "/users", { body: data });