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/state/useSettings.ts

@@ -0,0 +1,47 @@
+// Settings pages the admin may manage (D-21), server-filtered like the
+// navigation. The rail shows "Ustawienia" only when this list is non-empty.
+import { computed, readonly, ref } from 'vue'
+import { api } from '../api/client'
+import type { SettingsEntry } from '../api/types'
+
+const entries = ref<SettingsEntry[]>([])
+
+export const settings = readonly(entries)
+
+export const hasSettings = computed(() => entries.value.length > 0)
+
+export async function loadSettings(): Promise<SettingsEntry[]> {
+  const { data, response } = await api.GET('/settings')
+  entries.value = response.ok && data ? data.data : []
+  return entries.value
+}
+
+export function setSettings(next: SettingsEntry[]): void {
+  entries.value = next
+}
+
+export function settingsEntry(code: string): SettingsEntry | null {
+  return entries.value.find((entry) => entry.code === code) ?? null
+}
+
+/** Entries grouped by category, categories in first-seen order, by order. */
+export const settingsGroups = computed(() => {
+  const sorted = entries.value
+    .map((entry, index) => ({ entry, index }))
+    .sort((a, b) => a.entry.order - b.entry.order || a.index - b.index)
+    .map(({ entry }) => entry)
+  const groups: Array<{ category: string; entries: SettingsEntry[] }> = []
+  for (const entry of sorted) {
+    let group = groups.find((item) => item.category === entry.category)
+    if (!group) {
+      group = { category: entry.category, entries: [] }
+      groups.push(group)
+    }
+    group.entries.push(entry)
+  }
+  return groups
+})
+
+export function useSettings() {
+  return { settings, hasSettings, settingsGroups, loadSettings, settingsEntry }
+}