Redesign Wino Account login and registration dialogs (#835)

Add hero illustrations using XAML-native vector graphics (shield+lock
for login, person+plus badge for registration). Improve visual design
with gradient backgrounds, icon badges on benefit cards, and refined
spacing/corner radii. Add Enter key handling so pressing Enter in an
input field moves focus to the next field, and pressing Enter on the
last field triggers the primary action (login/register).

https://claude.ai/code/session_011B1M6UVeo4yUX3zNHBxQ2P

Co-authored-by: Claude <noreply@anthropic.com>

Wino.Mail.WinUI/Dialogs/WinoAccountLoginDialog.xaml.cs

@@ -1,5 +1,7 @@
 using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Controls;
+using Microsoft.UI.Xaml.Input;
+using Windows.System;
 using Wino.Core.Domain;
 using Wino.Core.Domain.Entities.Shared;
 using Wino.Core.Domain.Interfaces;
@@ -32,6 +34,25 @@ public sealed partial class WinoAccountLoginDialog : ContentDialog
 
         var deferral = args.GetDeferral();
 
+        try
+        {
+            await PerformLoginAsync();
+        }
+        finally
+        {
+            deferral.Complete();
+        }
+    }
+
+    private async System.Threading.Tasks.Task PerformLoginAsync()
+    {
+        var validationError = ValidateInput();
+        if (!string.IsNullOrWhiteSpace(validationError))
+        {
+            ShowError(validationError);
+            return;
+        }
+
         try
         {
             SetBusyState(true);
@@ -46,13 +67,11 @@ public sealed partial class WinoAccountLoginDialog : ContentDialog
             }
 
             Result = result.Account;
-            args.Cancel = false;
             Hide();
         }
         finally
         {
             SetBusyState(false);
-            deferral.Complete();
         }
     }
 
@@ -71,6 +90,24 @@ public sealed partial class WinoAccountLoginDialog : ContentDialog
         return string.Empty;
     }
 
+    private void EmailTextBox_KeyDown(object sender, KeyRoutedEventArgs e)
+    {
+        if (e.Key == VirtualKey.Enter)
+        {
+            PasswordBox.Focus(FocusState.Programmatic);
+            e.Handled = true;
+        }
+    }
+
+    private async void PasswordBox_KeyDown(object sender, KeyRoutedEventArgs e)
+    {
+        if (e.Key == VirtualKey.Enter)
+        {
+            e.Handled = true;
+            await PerformLoginAsync();
+        }
+    }
+
     private void InputChanged(TextBox sender, TextBoxTextChangingEventArgs args) => HideError();
 
     private void InputChanged(object sender, RoutedEventArgs e) => HideError();