Use Telegram Login Widget for web auth

lib/auth/telegram_login_button_web.dart

@@ -0,0 +1,76 @@
+import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
+import 'dart:ui_web' as ui_web;
+
+import 'package:flutter/widgets.dart';
+import 'package:web/web.dart' as web;
+
+import 'telegram_session_web.dart';
+
+const _telegramBotUsername = String.fromEnvironment(
+  'TELEGRAM_BOT_USERNAME',
+  defaultValue: 'carfteebot',
+);
+
+@JS('window')
+external JSObject get _window;
+
+class TelegramLoginButton extends StatefulWidget {
+  const TelegramLoginButton({required this.onAuthenticated, super.key});
+
+  final VoidCallback onAuthenticated;
+
+  @override
+  State<TelegramLoginButton> createState() => _TelegramLoginButtonState();
+}
+
+class _TelegramLoginButtonState extends State<TelegramLoginButton> {
+  late final String _callbackName =
+      'mapflowTelegramAuth${DateTime.now().microsecondsSinceEpoch}';
+  late final String _viewType = 'mapflow-telegram-login-$_callbackName';
+
+  @override
+  void initState() {
+    super.initState();
+    final callback = ((JSAny? user) {
+      saveTelegramLoginData(user);
+      if (mounted) {
+        widget.onAuthenticated();
+      }
+    }).toJS;
+    _window.setProperty(_callbackName.toJS, callback);
+    ui_web.platformViewRegistry.registerViewFactory(_viewType, _buildElement);
+  }
+
+  web.HTMLElement _buildElement(int viewId) {
+    final container = web.HTMLDivElement()
+      ..style.width = '100%'
+      ..style.height = '48px'
+      ..style.display = 'flex'
+      ..style.justifyContent = 'center'
+      ..style.alignItems = 'center';
+
+    final script = web.HTMLScriptElement()
+      ..src = 'https://telegram.org/js/telegram-widget.js?22'
+      ..async = true;
+
+    script
+      ..setAttribute('data-telegram-login', _telegramBotUsername)
+      ..setAttribute('data-size', 'large')
+      ..setAttribute('data-radius', '8')
+      ..setAttribute('data-userpic', 'false')
+      ..setAttribute('data-onauth', '$_callbackName(user)');
+
+    container.append(script);
+    return container;
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return SizedBox(
+      height: 48,
+      width: 240,
+      child: HtmlElementView(viewType: _viewType),
+    );
+  }
+}