feat: update main.dart with app initialization

lib/main.dart

@@ -0,0 +1,29 @@
+import 'package:flutter/material.dart';
+import 'package:traccar_client/main_screen.dart';
+import 'package:traccar_client/preferences.dart';
+
+void main() async {
+  WidgetsFlutterBinding.ensureInitialized();
+  await Preferences.init();
+  runApp(const TraccarClientApp());
+}
+
+class TraccarClientApp extends StatelessWidget {
+  const TraccarClientApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      title: 'Traccar Client',
+      debugShowCheckedModeBanner: false,
+      theme: ThemeData(
+        useMaterial3: true,
+        colorScheme: ColorScheme.fromSeed(seedColor: Colors.blue),
+        appBarTheme: const AppBarTheme(
+          centerTitle: true,
+        ),
+      ),
+      home: const MainScreen(),
+    );
+  }
+}