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/useSidebar.ts

@@ -0,0 +1,71 @@
+// Sidebar collapsed state (design: Navigation shell, Collapsed / tablet;
+// D-06, D-10). The section panel hides below about 1100px or when the admin
+// collapses it. The viewport only forces the collapse and never overwrites
+// the admin's own choice, which persists in localStorage as a boolean under
+// SIDEBAR_KEY. Nothing else is ever written to browser storage (T-10-22).
+import { computed, readonly, ref } from 'vue'
+
+export const SIDEBAR_KEY = 'summer-admin.sidebar'
+export const NARROW_QUERY = '(max-width: 1099px)'
+
+const manual = ref(false)
+const narrow = ref(false)
+
+/** The panel is hidden: forced by the viewport or chosen by the admin. */
+export const sidebarCollapsed = computed(() => narrow.value || manual.value)
+
+function storage(): Storage | null {
+  try {
+    return typeof window === 'undefined' ? null : window.localStorage
+  } catch {
+    return null
+  }
+}
+
+function readPreference(): boolean {
+  try {
+    return storage()?.getItem(SIDEBAR_KEY) === 'true'
+  } catch {
+    return false
+  }
+}
+
+/** Records the admin's choice; only 'true' or 'false' is stored. */
+export function setCollapsed(value: boolean): void {
+  manual.value = value
+  try {
+    storage()?.setItem(SIDEBAR_KEY, value ? 'true' : 'false')
+  } catch {
+    // Storage may be full or disabled; the choice still holds for the session.
+  }
+}
+
+/**
+ * Reads the stored preference and follows the viewport breakpoint. Returns
+ * the unsubscribe function; the shell calls it when it unmounts.
+ */
+export function watchViewport(): () => void {
+  manual.value = readPreference()
+  if (typeof window === 'undefined' || typeof window.matchMedia !== 'function') {
+    narrow.value = false
+    return () => undefined
+  }
+  const query = window.matchMedia(NARROW_QUERY)
+  narrow.value = query.matches
+  const onChange = (event: MediaQueryListEvent): void => {
+    narrow.value = event.matches
+  }
+  query.addEventListener('change', onChange)
+  return () => query.removeEventListener('change', onChange)
+}
+
+export function useSidebar() {
+  return {
+    collapsed: sidebarCollapsed,
+    /** The viewport is below the breakpoint; expanding is not possible. */
+    narrow: readonly(narrow),
+    manual: readonly(manual),
+    setCollapsed,
+    watchViewport,
+  }
+}