feat(10-04): collapsible panel with flyout, user menu with logout, breadcrumbs and dark mode

- useSidebar: collapsed below 1100px (matchMedia) or by the admin's choice,
  persisted as a boolean under summer-admin.sidebar; the viewport never
  overwrites the stored choice
- SectionPanel collapse and rail expand buttons; SectionFlyout (role menu)
  opens on hover, focus, Enter or ArrowDown on a rail item, closes on Esc or
  about 200 ms after leaving and returns focus to the rail item
- Breadcrumbs with plugin, controller and record crumbs; UserMenu (Reka
  DropdownMenu) with initials, name, role and Wyloguj
- useAuth.logout POSTs /auth/logout, clears user, navigation and settings
  and routes to login even when the call fails
- applyColorScheme toggles .dark from prefers-color-scheme (no toggle, A6)
- newest toast first, 200 ms fade and scale for dialogs and toasts
- one relation-manager type constant in the registry
- shell smoke tests; tests default to a desktop, light matchMedia

admin/src/components/form/FormGrid.vue

@@ -1,6 +1,7 @@
 <script setup lang="ts">
 import type { AdminRecord, ControllerParams, FormField as FormFieldSchema, RecordMeta } from '../../api/types'
 import FormField from './FormField.vue'
+import { RELATION_MANAGER } from './registry'
 
 // Two-column form grid (design screen 4): span left -> column 1, right ->
 // column 2, full (Winter's default) -> the whole row, auto and row -> the next
@@ -18,7 +19,7 @@ const emit = defineEmits<{ update: [name: string, value: unknown] }>()
 
 function spanClass(field: FormFieldSchema): string {
   // The relation manager always takes the whole row (design screen 5).
-  if (field.type === 'relation-manager') {
+  if (field.type === RELATION_MANAGER) {
     return 'col-span-full'
   }
   switch (field.span) {