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/state/useBreadcrumbs.ts

@@ -0,0 +1,16 @@
+// The record crumb of the header breadcrumbs (design: Top header). The form
+// view owns the record's title; it publishes it here while it is mounted so
+// the shell can show "Plugin › Controller › Record".
+import { readonly, ref } from 'vue'
+
+const record = ref('')
+
+export const recordCrumb = readonly(record)
+
+export function setRecordCrumb(label: string): void {
+  record.value = label
+}
+
+export function clearRecordCrumb(): void {
+  record.value = ''
+}