added chat app

Chat-App/lib/main.dart

@@ -0,0 +1,27 @@
+import 'package:flutter/material.dart';
+import 'package:ai_chat_lab/screens/startup_screen.dart';
+
+void main() {
+  runApp(const MainApp());
+}
+
+class MainApp extends StatelessWidget {
+  const MainApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      title: 'Convai Chat',
+      theme: ThemeData(
+        colorScheme: ColorScheme.fromSeed(
+          seedColor: const Color(0xFF4F8CFF),
+          brightness: Brightness.light,
+        ),
+        useMaterial3: true,
+        fontFamily: 'Segoe UI',
+      ),
+      home: const StartupScreen(),
+      debugShowCheckedModeBanner: false,
+    );
+  }
+}