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/main.ts

@@ -3,12 +3,15 @@ import App from './App.vue'
 import { createAdminRouter } from './app/router'
 import { onUnauthorized } from './api/client'
 import { loadStrings } from './app/i18n'
+import { applyColorScheme } from './app/theme'
 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> {
+  // Dark mode follows the system preference before anything renders (A6).
+  applyColorScheme()
   // Boot order (research Pattern 7): the public strings bundle first, so the
   // login screen is translated, then the session, then navigation.
   await loadStrings().catch(() => undefined)