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/screens/auth_gate.dart

@@ -0,0 +1,30 @@
+import 'package:firebase_auth/firebase_auth.dart';
+import 'package:flutter/material.dart';
+
+import '../services/auth_service.dart';
+import 'home_screen.dart';
+import 'login_screen.dart';
+
+class AuthGate extends StatelessWidget {
+  const AuthGate({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return StreamBuilder<User?>(
+      stream: AuthService.instance.authStateChanges(),
+      builder: (context, snapshot) {
+        if (snapshot.connectionState == ConnectionState.waiting) {
+          return const Scaffold(
+            body: Center(child: CircularProgressIndicator()),
+          );
+        }
+
+        if (snapshot.hasData) {
+          return const HomeScreen();
+        }
+
+        return const LoginScreen();
+      },
+    );
+  }
+}