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/main.ts

@@ -5,6 +5,7 @@ import { onUnauthorized } from './api/client'
 import { loadStrings } from './app/i18n'
 import { clearUser, me } from './state/useAuth'
 import { loadNavigation } from './state/useNavigation'
+import { loadSettings } from './state/useSettings'
 import './styles/main.css'
 
 async function boot(): Promise<void> {
@@ -15,7 +16,7 @@ async function boot(): Promise<void> {
   // visitor to the login route with the requested path as redirect.
   const user = await me().catch(() => null)
   if (user) {
-    await loadNavigation().catch(() => [])
+    await Promise.all([loadNavigation().catch(() => []), loadSettings().catch(() => [])])
   }
   const router = createAdminRouter()
   onUnauthorized(() => {