added 3 screen mod to login

lib/view_models/login_view_model.dart

@@ -0,0 +1,42 @@
+// lib/view_models/login_view_model.dart
+import 'package:flutter/material.dart';
+
+class LoginViewModel with ChangeNotifier {
+  final TextEditingController usernameController = TextEditingController();
+  final TextEditingController passwordController = TextEditingController();
+
+  final FocusNode usernameFocus = FocusNode();
+  final FocusNode passwordFocus = FocusNode();
+
+  bool _obscurePassword = true;
+
+  LoginViewModel() {
+    usernameController.addListener(_onTextChanged);
+    passwordController.addListener(_onTextChanged);
+    usernameFocus.addListener(_onTextChanged);
+    passwordFocus.addListener(_onTextChanged);
+  }
+
+  bool get obscurePassword => _obscurePassword;
+  bool get isLoginEnabled =>
+      usernameController.text.isNotEmpty &&
+      passwordController.text.isNotEmpty;
+
+  void togglePasswordVisibility() {
+    _obscurePassword = !_obscurePassword;
+    notifyListeners();
+  }
+
+  void _onTextChanged() {
+    notifyListeners();
+  }
+
+  @override
+  void dispose() {
+    usernameController.dispose();
+    passwordController.dispose();
+    usernameFocus.dispose();
+    passwordFocus.dispose();
+    super.dispose();
+  }
+}