feat: introduce app configuration

- Add AppConfig class
- Define environment variables
- Add factory constructors

Author: fulleni

lib/app/config/app_config.dart

@@ -0,0 +1,28 @@
+import 'package:ht_main/app/config/app_environment.dart';
+
+class AppConfig {
+  const AppConfig({
+    required this.environment,
+    required this.baseUrl,
+    // Add other environment-specific configs here (e.g., analytics keys)
+  });
+
+  final AppEnvironment environment;
+  final String baseUrl;
+
+  // Factory constructors for different environments
+  factory AppConfig.production() => const AppConfig(
+        environment: AppEnvironment.production,
+        baseUrl: 'http://api.yourproductiondomain.com', // Replace with actual production URL
+      );
+
+  factory AppConfig.developmentInMemory() => const AppConfig(
+        environment: AppEnvironment.developmentInMemory,
+        baseUrl: 'http://localhost:8080', // Base URL still needed for Auth API client, even if data is in-memory
+      );
+
+  factory AppConfig.developmentApi() => const AppConfig( // New: For local Dart Frog API
+        environment: AppEnvironment.developmentApi,
+        baseUrl: 'http://localhost:8080', // Default Dart Frog local URL
+      );
+}