switch token script to implicit flow and fix interceptor hanging Future

The script used authorization code flow (response_type=code) which produces
tokens expiring in ~4 hours, while the app uses implicit flow (~60 days).
Switched the script to implicit flow to match, removing the client_secret
requirement and token exchange step.

Also fixed UnauthorizedInterceptor swallowing 401 errors without calling
handler.reject(), which left Dio request Futures hanging forever.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/apis/unauthorized_interceptor.dart

@@ -22,8 +22,9 @@ class UnauthorizedInterceptor extends Interceptor {
         return;
       }
 
-      // For other requests, show login dialog and don't propagate
+      // For other requests, show login dialog and reject so the Future completes
       _showLoginDialog();
+      handler.reject(err);
       return;
     }