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/services/auth_service.dart

@@ -0,0 +1,48 @@
+import 'package:firebase_auth/firebase_auth.dart';
+
+class AuthService {
+  AuthService._();
+
+  static final AuthService instance = AuthService._();
+  final FirebaseAuth _auth = FirebaseAuth.instance;
+
+  Stream<User?> authStateChanges() => _auth.authStateChanges();
+
+  User? get currentUser => _auth.currentUser;
+
+  Future<UserCredential> signInWithEmailPassword({
+    required String email,
+    required String password,
+  }) {
+    return _auth.signInWithEmailAndPassword(email: email, password: password);
+  }
+
+  Future<UserCredential> registerWithEmailPassword({
+    required String email,
+    required String password,
+  }) {
+    return _auth.createUserWithEmailAndPassword(
+      email: email,
+      password: password,
+    );
+  }
+
+  Future<void> sendPasswordResetEmail(String email) {
+    return _auth.sendPasswordResetEmail(email: email);
+  }
+
+  Future<UserCredential> signInWithGoogle() {
+    final provider = GoogleAuthProvider();
+    provider.setCustomParameters({'prompt': 'select_account'});
+    return _auth.signInWithPopup(provider);
+  }
+
+  Future<UserCredential> signInWithGithub() {
+    final provider = GithubAuthProvider();
+    return _auth.signInWithPopup(provider);
+  }
+
+  Future<void> signOut() {
+    return _auth.signOut();
+  }
+}