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>

pubspec.yaml

@@ -0,0 +1,25 @@
+name: flutter_ecommerce_portal
+description: Dockerized Flutter web e-commerce portal with Firebase auth
+publish_to: 'none'
+version: 1.0.0+1
+
+environment:
+  sdk: '>=3.4.0 <4.0.0'
+
+dependencies:
+  flutter:
+    sdk: flutter
+  cupertino_icons: ^1.0.8
+  firebase_core: ^3.8.0
+  firebase_auth: ^5.3.3
+  provider: ^6.1.2
+
+dev_dependencies:
+  flutter_test:
+    sdk: flutter
+  flutter_lints: ^4.0.0
+
+flutter:
+  uses-material-design: true
+  assets:
+    - assets/config/runtime_config.json