refactor entire frontend

frontend/lib/login_screen.dart

@@ -0,0 +1,41 @@
+import 'package:flutter/material.dart';
+
+class LoginScreen extends StatelessWidget {
+  final Function(String, String) onLogin;
+
+  LoginScreen({required this.onLogin});
+
+  final TextEditingController usernameController = TextEditingController();
+  final TextEditingController passwordController = TextEditingController();
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(title: Text('Login')),
+      body: Center(
+        child: Padding(
+          padding: const EdgeInsets.all(16.0),
+          child: Column(
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: [
+              TextField(controller: usernameController, decoration: InputDecoration(labelText: 'Username')),
+              SizedBox(height: 20),
+              TextField(
+                controller: passwordController,
+                decoration: InputDecoration(labelText: 'Password'),
+                obscureText: true, // Hide password characters
+              ),
+              SizedBox(height: 20),
+              ElevatedButton(
+                onPressed: () {
+                  onLogin(usernameController.text, passwordController.text);
+                },
+                child: Text('Login'),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}