user form, backup: two gaps the mockup comparison found

Owner, 2026-10-18: "Что ещё из макетов мы также прошляпили?" - every mockup
held against the panel; two small gaps beyond the queues:

- user.html: with All ticked, a list's single domains are disabled
  (mockup user.html:34-36). A panel.js show-when rule with disable: the
  boxes data-single-out / data-single-in follow data-all-out / data-all-in,
  at load and on change; a disabled box is not submitted, which the server
  ignores with All anyway. node test testdata/alldomains_test.js (fails on
  the previous panel.js).
- backup.html: "domain's settings" is a link, to Outbound › Domains (mockup
  backup.html:35 links a domain's settings; a server page has no one domain).

Tests: go test ./internal/web/... pass, TestPanelJS with node 24.

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

internal/web/view/templates/backup.html

@@ -34,7 +34,7 @@
   <div class="column is-6">
 {{template "box_open" .Import}}
 {{template "body_open"}}
-<p class="mb-3">A domain export from another instance — plain <code>.json</code> or encrypted <code>.spde</code>. Its DKIM key and application passwords come across, so the published DNS needs no change. The export itself is made on the domain's settings page.</p>
+<p class="mb-3">A domain export from another instance — plain <code>.json</code> or encrypted <code>.spde</code>. Its DKIM key and application passwords come across, so the published DNS needs no change. The export itself is made on the <a href="/outbound/domains">domain's settings</a>.</p>
 <form class="sp-form" method="post" action="{{.ImportAction}}" enctype="multipart/form-data">
   <div class="field"><label class="label" for="importfile">Domain export file</label>
     <div class="file has-name is-fullwidth"><label class="file-label"><input class="file-input" id="importfile" name="file" type="file" accept=".json,.spde,application/json" required data-import-file><span class="file-cta"><i class="ti ti-upload"></i><span class="file-label ml-2">Choose a file…</span></span><span class="file-name">No file chosen</span></label></div></div>