Refactor authentication handling and update loading components

The authentication handling logic in the middleware.ts file was refactored to improve clarity and control flow. In addition, the loading component, previously located in the main app directory, has been deleted and recreated specifically for admin use. The list of private path prefixes has been updated in the use-auth-change-listener.ts file to reflect these changes.

apps/web/app/admin/loading.tsx

@@ -0,0 +1,3 @@
+import { GlobalLoader } from '@kit/ui/global-loader';
+
+export default GlobalLoader;