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/app/router.ts

@@ -5,6 +5,8 @@ import { homePath } from '../state/useNavigation'
 import LoginView from '../views/LoginView.vue'
 import ListView from '../views/ListView.vue'
 import FormView from '../views/FormView.vue'
+import SettingsFormView from '../views/SettingsFormView.vue'
+import SettingsIndexView from '../views/SettingsIndexView.vue'
 import NotFoundView from '../views/NotFoundView.vue'
 
 declare module 'vue-router' {
@@ -43,6 +45,8 @@ export function createAdminRouter(history: RouterHistory = createWebHistory(runt
         meta: { shell: true },
         beforeEnter: () => homePath() ?? true,
       },
+      { path: '/settings', name: 'settings', component: SettingsIndexView, meta: { shell: true } },
+      { path: '/settings/:code', name: 'settings-form', component: SettingsFormView, meta: { shell: true } },
       { path: '/:vendor/:plugin/:controller', name: 'list', component: ListView, meta: { shell: true } },
       { path: '/:vendor/:plugin/:controller/create', name: 'create', component: FormView, meta: { shell: true } },
       { path: '/:vendor/:plugin/:controller/:id(\\d+)', name: 'record', component: FormView, meta: { shell: true } },