Use Telegram Login Widget for web auth

lib/auth/telegram_login_button_stub.dart

@@ -0,0 +1,12 @@
+import 'package:flutter/material.dart';
+
+class TelegramLoginButton extends StatelessWidget {
+  const TelegramLoginButton({required this.onAuthenticated, super.key});
+
+  final VoidCallback onAuthenticated;
+
+  @override
+  Widget build(BuildContext context) {
+    return const FilledButton(onPressed: null, child: Text('Telegram'));
+  }
+}