feat(10-03): tabs, toggles, relation fields, form lifecycle and settings pages

- FormTabs groups fields by tab (untabbed fields in the default tab) as a
  segmented tablist; a tab holding invalid fields after a 422 shows a
  count badge and the form switches to the first invalid field
- switch, checkbox and relation join the renderer registry: toggle cards
  (role=switch, 20px checkbox) keep a numeric value numeric; relation
  fields are read-only labels from meta.labels, a searchable single
  select over fields/{field}/options with emptyOption first, or ordered
  removable chips with an appending search (300 ms debounce, 20 per
  page, more on scroll or the more action)
- FormView gets the back button, record title and update subtitle, a
  sticky footer (Usuń with deleteConfirm then DELETE, Anuluj, Zapisz i
  zamknij to the mapped redirectClose, Zapisz), and asks before leaving a
  dirty form on any route change plus a beforeunload guard
- Settings: the rail pins Ustawienia to the bottom when /settings is
  non-empty; /settings lists pages by category; /settings/:code renders
  the settings schema through FormGrid and the registry, PUTs the values
  and maps a 422 like the record form
- New backend::lang keys (form.more_options, tab_default, discard,
  settings.back); form and settings smoke tests; boardwalk/dist rebuilt

admin/src/components/shell/AppShell.vue

@@ -45,7 +45,10 @@ const initials = computed(() =>
     <div class="flex min-w-0 flex-1 flex-col">
       <header class="flex h-header shrink-0 items-center justify-between border-b border-border bg-surface pr-6 pl-8">
         <nav :aria-label="t('backend::lang.nav.breadcrumbs')" class="flex items-center gap-2">
-          <template v-if="active">
+          <span v-if="route.name === 'settings' || route.name === 'settings-form'" class="font-semibold">
+            {{ t('backend::lang.nav.settings') }}
+          </span>
+          <template v-else-if="active">
             <span :class="section ? 'text-muted' : 'font-semibold'">{{ active.label }}</span>
             <template v-if="section">
               <ChevronRight :size="14" class="text-muted" aria-hidden="true" />