Add per-account folder customization page (#855)

Introduce a dedicated settings page that lets users reorder, hide,
and pin/unpin folders per account. Folders are organized into Pinned,
Categories (Gmail only), and More sections with drag-to-reorder via
ListView. New Order column on MailItemFolder persists the custom
layout; the default sort falls back to alphabetic when no custom
order is set. A reset action wipes all customization in a single
transaction and restores system-folder stickiness.

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

Wino.Mail.WinUI/Views/Account/FolderCustomizationPage.xaml.cs

@@ -0,0 +1,38 @@
+using System.Collections.ObjectModel;
+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Controls;
+using Wino.Mail.ViewModels.Data;
+using Wino.Views.Abstract;
+
+namespace Wino.Views;
+
+public sealed partial class FolderCustomizationPage : FolderCustomizationPageAbstract
+{
+    public FolderCustomizationPage()
+    {
+        InitializeComponent();
+    }
+
+    private async void ListView_DropCompleted(UIElement sender, Microsoft.UI.Xaml.Controls.Primitives.DropCompletedEventArgs args)
+    {
+        // ListView.CanReorderItems automatically mutates the backing
+        // ObservableCollection; persist the new order here.
+        await ViewModel.PersistLayoutAsync();
+    }
+
+    private async void PinToggle_Click(object sender, RoutedEventArgs e)
+    {
+        if (sender is FrameworkElement element && element.DataContext is FolderCustomizationItemViewModel item)
+        {
+            await ViewModel.TogglePinAsync(item);
+        }
+    }
+
+    private async void HideToggle_Click(object sender, RoutedEventArgs e)
+    {
+        if (sender is FrameworkElement element && element.DataContext is FolderCustomizationItemViewModel item)
+        {
+            await ViewModel.ToggleHiddenAsync(item);
+        }
+    }
+}