feat(authentication): add responsive authentication layout

- Create AuthLayout widget for centering and constraining authentication content
- Enable scrolling for smaller screens
- Improve visual experience on larger screens

Author: fulleni

lib/authentication/widgets/auth_layout.dart

@@ -0,0 +1,33 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_news_app_web_dashboard_full_source_code/shared/constants/app_constants.dart';
+import 'package:ui_kit/ui_kit.dart';
+
+/// {@template auth_layout}
+/// A responsive layout for authentication pages.
+///
+/// It centers the content and constrains its width for a better
+/// visual experience on larger screens, while allowing it to be
+/// scrollable on smaller screens.
+/// {@endtemplate}
+class AuthLayout extends StatelessWidget {
+  /// {@macro auth_layout}
+  const AuthLayout({required this.child, super.key});
+
+  /// The child widget to display within the layout.
+  final Widget child;
+
+  @override
+  Widget build(BuildContext context) {
+    return Padding(
+      padding: const EdgeInsets.all(AppSpacing.lg),
+      child: Center(
+        child: ConstrainedBox(
+          constraints: const BoxConstraints(
+            maxWidth: AppConstants.kMaxAuthWidth,
+          ),
+          child: SingleChildScrollView(child: child),
+        ),
+      ),
+    );
+  }
+}