fix(admin): isolate login on admin host

Allow runtime request headers through API preflight and keep the storefront shell hidden while admin QR authentication gates backoffice.

src/app/app.html

@@ -10,6 +10,8 @@
     <p>{{ 'app.serverError' | translate }}</p>
     <button class="retry-btn" (click)="retryConnection()">{{ 'app.retryConnection' | translate }}</button>
   </div>
+} @else if (isAdminHost && !isAdminRoute()) {
+  <app-telegram-login mode="admin" />
 } @else if (isAdminRoute()) {
   <router-outlet></router-outlet>
   <app-telegram-login mode="admin" />
@@ -30,4 +32,4 @@
   }
   <!-- <app-telegram-login /> -->
   <app-telegram-login mode="admin" />
-}
+}