Initialize project and update portal port configuration

Set default portal port to 8081, fix Dart build issue in cart screen, and update setup documentation.

Co-Authored-By: Oz <oz-agent@warp.dev>

lib/main.dart

@@ -0,0 +1,34 @@
+import 'package:flutter/material.dart';
+import 'package:provider/provider.dart';
+
+import 'screens/auth_gate.dart';
+import 'services/app_config_service.dart';
+import 'services/cart_service.dart';
+
+Future<void> main() async {
+  WidgetsFlutterBinding.ensureInitialized();
+  await AppConfigService.instance.initialize();
+  runApp(const EcommercePortalApp());
+}
+
+class EcommercePortalApp extends StatelessWidget {
+  const EcommercePortalApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return MultiProvider(
+      providers: [
+        ChangeNotifierProvider(create: (_) => CartService()),
+      ],
+      child: MaterialApp(
+        debugShowCheckedModeBanner: false,
+        title: 'Flutter E-Commerce Portal',
+        theme: ThemeData(
+          colorScheme: ColorScheme.fromSeed(seedColor: Colors.indigo),
+          useMaterial3: true,
+        ),
+        home: const AuthGate(),
+      ),
+    );
+  }
+}