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/handlers/handlers_delegation_test.go

@@ -431,7 +431,7 @@ func TestUserFormAssignsBothDirections(t *testing.T) {
 	body := send(h.HandleUserEdit, &root, "GET", "/server/users/"+idStr(other.ID), map[string]string{"uid": idStr(other.ID)}, nil).Body.String()
 	for _, want := range []string{
 		`name="all_domains"`, `name="all_inbound_domains"`, "out.example.com",
-		`name="inbound_domain_ids" value="` + idStr(in.ID) + `" checked`,
+		`name="inbound_domain_ids" value="` + idStr(in.ID) + `" data-single-in checked`,
 	} {
 		if !strings.Contains(body, want) {
 			t.Errorf("the user form is missing %q", want)