Implemented country registration handling in the API, allowing for dynamic country selection in the login and country selection screens. Added parsing logic for registration countries and updated the UI to reflect allowed countries based on the API response.

lib/backend/api.dart

@@ -2,6 +2,7 @@ import 'dart:async';
 import 'dart:typed_data';
 
 import '../core/config/config.dart';
+import '../core/config/countries.dart';
 import '../core/protocol/opcode_map.dart';
 import '../core/protocol/packet.dart';
 import '../core/transport/connection.dart';
@@ -33,6 +34,11 @@ class Api {
 
   Map<dynamic, dynamic>? get userAgent => _userAgent;
 
+  List<CountryName>? _registrationCountries;
+
+  List<CountryName> get registrationCountries =>
+      _registrationCountries ?? allCountries;
+
   Stream<SessionState> get stateStream => _stateController.stream;
   SessionState get state => _sessionState;
 
@@ -76,6 +82,7 @@ class Api {
     try {
       final response = await sendHandshake();
       if (response.isOk) {
+        _registrationCountries = _parseRegistrationCountries(response.payload);
         _setSessionState(SessionState.online);
         _startPinging();
         logger.i('Сессия онлайн, хэндшейк ок');
@@ -230,6 +237,28 @@ class Api {
     });
   }
 
+  static List<CountryName>? _parseRegistrationCountries(dynamic payload) {
+    if (payload is! Map) return null;
+    final raw = payload['reg-country-code'];
+    if (raw is! List || raw.isEmpty) return null;
+    final codes = <String>[];
+    for (final e in raw) {
+      if (e is String && e.isNotEmpty) codes.add(e.toUpperCase());
+    }
+    if (codes.isEmpty) return null;
+    var list = countriesInServerOrder(codes);
+    if (list.isEmpty) return null;
+
+    final loc = payload['location'];
+    if (loc is String && loc.length == 2) {
+      final home = countriesByCode[loc.toUpperCase()];
+      if (home != null && !list.any((c) => c.code == home.code)) {
+        list = [home, ...list];
+      }
+    }
+    return list;
+  }
+
   void _scheduleReconnect() {
     if (_reconnectAttempts >= ServerConfig.maxReconnectAttempts) {
       logger.e('Лимит попыток реконнекта');