feat: Implement initial authentication, multi-environment support, and core app infrastructure.

lib/core/network/api_client.dart

@@ -0,0 +1,92 @@
+import 'package:dio/dio.dart';
+import 'package:real_estate_mobile/config/app_config.dart';
+import 'package:real_estate_mobile/core/network/api_exceptions.dart';
+import 'package:real_estate_mobile/core/storage/secure_storage.dart';
+
+class ApiClient {
+  static ApiClient? _instance;
+  late final Dio _dio;
+
+  ApiClient._() {
+    _dio = Dio(
+      BaseOptions(
+        baseUrl: AppConfig.apiBaseUrl,
+        connectTimeout: const Duration(seconds: 30),
+        receiveTimeout: const Duration(seconds: 30),
+        headers: {
+          'Content-Type': 'application/json',
+          'Accept': 'application/json',
+        },
+      ),
+    );
+
+    _dio.interceptors.addAll([
+      _authInterceptor(),
+      _errorInterceptor(),
+    ]);
+  }
+
+  static ApiClient get instance {
+    _instance ??= ApiClient._();
+    return _instance!;
+  }
+
+  Dio get dio => _dio;
+
+  InterceptorsWrapper _authInterceptor() {
+    return InterceptorsWrapper(
+      onRequest: (options, handler) async {
+        final token = await SecureStorage.getAccessToken();
+        if (token != null) {
+          options.headers['Authorization'] = 'Bearer $token';
+        }
+        handler.next(options);
+      },
+    );
+  }
+
+  InterceptorsWrapper _errorInterceptor() {
+    return InterceptorsWrapper(
+      onError: (error, handler) {
+        final response = error.response;
+        if (response != null) {
+          final data = response.data;
+          if (data is Map<String, dynamic>) {
+            final message = data['message'] is List
+                ? (data['message'] as List).join(', ')
+                : data['message']?.toString() ?? 'An error occurred';
+
+            final errors = (data['errors'] as List<dynamic>?)
+                    ?.map((e) => FieldError.fromJson(e as Map<String, dynamic>))
+                    .toList() ??
+                [];
+
+            handler.reject(
+              DioException(
+                requestOptions: error.requestOptions,
+                response: error.response,
+                error: ApiException(
+                  message: message,
+                  statusCode: response.statusCode,
+                  fieldErrors: errors,
+                ),
+              ),
+            );
+            return;
+          }
+        }
+
+        handler.reject(
+          DioException(
+            requestOptions: error.requestOptions,
+            response: error.response,
+            error: ApiException(
+              message: error.message ?? 'Network error occurred',
+              statusCode: response?.statusCode,
+            ),
+          ),
+        );
+      },
+    );
+  }
+}

lib/core/network/api_exceptions.dart

@@ -0,0 +1,31 @@
+class ApiException implements Exception {
+  final String message;
+  final int? statusCode;
+  final List<FieldError> fieldErrors;
+
+  const ApiException({
+    required this.message,
+    this.statusCode,
+    this.fieldErrors = const [],
+  });
+
+  @override
+  String toString() => 'ApiException: $message (status: $statusCode)';
+}
+
+class FieldError {
+  final String field;
+  final List<String> errors;
+
+  const FieldError({required this.field, required this.errors});
+
+  factory FieldError.fromJson(Map<String, dynamic> json) {
+    return FieldError(
+      field: json['field'] as String? ?? '',
+      errors: (json['errors'] as List<dynamic>?)
+              ?.map((e) => e.toString())
+              .toList() ??
+          [],
+    );
+  }
+}