Multiple improvements in authentication functionality

frontend/lib/login_screen.dart

@@ -8,6 +8,13 @@ class LoginScreen extends StatelessWidget {
   final TextEditingController usernameController = TextEditingController();
   final TextEditingController passwordController = TextEditingController();
 
+  final FocusNode usernameFocusNode = FocusNode();
+  final FocusNode passwordFocusNode = FocusNode();
+
+  void _handleLogin() {
+    onLogin(usernameController.text, passwordController.text);
+  }
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(
@@ -18,18 +25,29 @@ class LoginScreen extends StatelessWidget {
           child: Column(
             mainAxisAlignment: MainAxisAlignment.center,
             children: [
-              TextField(controller: usernameController, decoration: InputDecoration(labelText: 'Username')),
+              TextField(
+                controller: usernameController,
+                focusNode: usernameFocusNode,
+                decoration: InputDecoration(labelText: 'Username'),
+                textInputAction: TextInputAction.next,
+                onSubmitted: (_) {
+                  FocusScope.of(context).requestFocus(passwordFocusNode);
+                },
+              ),
               SizedBox(height: 20),
               TextField(
                 controller: passwordController,
+                focusNode: passwordFocusNode,
                 decoration: InputDecoration(labelText: 'Password'),
-                obscureText: true, // Hide password characters
+                obscureText: true,
+                textInputAction: TextInputAction.done,
+                onSubmitted: (_) {
+                  _handleLogin();
+                },
               ),
               SizedBox(height: 20),
               ElevatedButton(
-                onPressed: () {
-                  onLogin(usernameController.text, passwordController.text);
-                },
+                onPressed: _handleLogin,
                 child: Text('Login'),
               ),
             ],