fix: Update nginx config to use dynamic DNS resolution

- Replace upstream blocks with resolver directive
- Use variables for backend addresses to avoid startup errors
- Simplify configuration with single server block
- Add health check endpoint

lib/core/nanaxe_server_service.dart

@@ -12,7 +12,7 @@ class NanaxeServerService {
 
   String? _baseUrl;
   String? _authToken;
-  
+
   static const String _prefsUrlKey = 'nanaxe_server_url';
   static const String _prefsTokenKey = 'nanaxe_server_token';
 
@@ -25,9 +25,10 @@ class NanaxeServerService {
 
   /// Настройка сервера
   Future<void> configure(String baseUrl, {String? token}) async {
-    _baseUrl = baseUrl.replaceAll(RegExp(r'/+$'), ''); // Remove trailing slashes
+    _baseUrl =
+        baseUrl.replaceAll(RegExp(r'/+$'), ''); // Remove trailing slashes
     _authToken = token;
-    
+
     final prefs = await SharedPreferences.getInstance();
     await prefs.setString(_prefsUrlKey, _baseUrl!);
     if (token != null) {
@@ -39,7 +40,7 @@ class NanaxeServerService {
   Future<void> clearConfiguration() async {
     _baseUrl = null;
     _authToken = null;
-    
+
     final prefs = await SharedPreferences.getInstance();
     await prefs.remove(_prefsUrlKey);
     await prefs.remove(_prefsTokenKey);
@@ -54,7 +55,8 @@ class NanaxeServerService {
   // ==================== AUTH ====================
 
   /// Регистрация нового пользователя
-  Future<Map<String, dynamic>> register(String email, String password, String username) async {
+  Future<Map<String, dynamic>> register(
+      String email, String password, String username) async {
     if (_baseUrl == null) throw Exception('Server not configured');
 
     final response = await http.post(
@@ -68,7 +70,7 @@ class NanaxeServerService {
     );
 
     final data = jsonDecode(response.body);
-    
+
     if (response.statusCode == 201) {
       _authToken = data['token'];
       final prefs = await SharedPreferences.getInstance();
@@ -93,7 +95,7 @@ class NanaxeServerService {
     );
 
     final data = jsonDecode(response.body);
-    
+
     if (response.statusCode == 200) {
       _authToken = data['token'];
       final prefs = await SharedPreferences.getInstance();
@@ -323,11 +325,11 @@ class NanaxeServerService {
     final headers = {
       'Content-Type': 'application/json',
     };
-    
+
     if (_authToken != null) {
       headers['Authorization'] = 'Bearer $_authToken';
     }
-    
+
     return headers;
   }