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/app/theme.ts

@@ -0,0 +1,25 @@
+// Colour scheme (D-06, flagged assumption A6): the admin follows the system
+// preference only, with no toggle. The .dark class on the document element
+// swaps the design's dark tokens in main.css; the sidebar stays dark in both
+// modes and gains its #222b40 right border in dark mode.
+export const DARK_QUERY = '(prefers-color-scheme: dark)'
+
+/**
+ * Applies the current preference and follows changes. Returns the
+ * unsubscribe function.
+ */
+export function applyColorScheme(win: Window = window): () => void {
+  const root = win.document.documentElement
+  if (typeof win.matchMedia !== 'function') {
+    root.classList.remove('dark')
+    return () => undefined
+  }
+  const query = win.matchMedia(DARK_QUERY)
+  const apply = (dark: boolean): void => {
+    root.classList.toggle('dark', dark)
+  }
+  apply(query.matches)
+  const onChange = (event: MediaQueryListEvent): void => apply(event.matches)
+  query.addEventListener('change', onChange)
+  return () => query.removeEventListener('change', onChange)
+}