feat: Enforce portrait orientation across platforms and switch Android Fastlane deployment from APK to AAB.

lib/main.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:firebase_core/firebase_core.dart';
 import 'package:travel_mate/blocs/balance/balance_bloc.dart';
@@ -47,6 +48,10 @@ import 'package:intl/date_symbol_data_local.dart';
 /// initializes Firebase, and starts the application.
 void main() async {
   WidgetsFlutterBinding.ensureInitialized();
+  await SystemChrome.setPreferredOrientations([
+    DeviceOrientation.portraitUp,
+    DeviceOrientation.portraitDown,
+  ]);
   await dotenv.load(fileName: ".env");
   await Firebase.initializeApp(options: DefaultFirebaseOptions.currentPlatform);
   await initializeDateFormatting('fr_FR', null);