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/app.html

@@ -25,4 +25,5 @@
     <div class="footer-placeholder" aria-hidden="true"></div>
   }
   <!-- <app-telegram-login /> -->
+  <app-admin-login />
 }