feat(sprint18): editor autosave/reset, admin auth, QR reuse, Ed25519 prep

- Project editor: persist draft to localStorage, restore on reload,
  last-saved/draft-restored status indicators, section/whole-draft reset
  with confirmation.
- Extract shared QR/polling/expiry engine from TelegramLoginComponent
  (shared/qr-login) and reuse it for a new admin login flow.
- Admin authentication kept fully separate from customer session:
  own cookie/localStorage keys, signals, guard, and header interceptor
  (core/admin-auth).
- ?login=true / ?adminLogin=true open the respective login dialog for
  manual testing.
- Ed25519 challenge/verify interfaces (fail-closed no-op binding) ready
  for backend delivery.
- Document autosave/reset/admin-auth/QR-reuse/Ed25519 model and the
  remaining full-field-coverage gap in docs/Project-Editor.md.

src/app/models/admin-auth.model.ts

@@ -0,0 +1,16 @@
+export interface AdminSession {
+  sessionId: string;
+  adminId: number | null;
+  username: string | null;
+  displayName: string;
+  role: string | null;
+  active: boolean;
+  expires: string;
+}
+
+export interface AdminWebSessionStart {
+  webSessionID: string;
+  url: string;
+}
+
+export type AdminAuthStatus = 'unknown' | 'checking' | 'authenticated' | 'expired' | 'unauthenticated';