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/App.xaml.cs

@@ -368,6 +368,7 @@ public partial class App : WinoApplication,
 
         services.AddTransient(typeof(ImapCalDavSettingsPageViewModel));
         services.AddTransient(typeof(AccountDetailsPageViewModel));
+        services.AddTransient(typeof(FolderCustomizationPageViewModel));
         services.AddTransient(typeof(SignatureManagementPageViewModel));
         services.AddTransient(typeof(MessageListPageViewModel));
         services.AddTransient(typeof(MailNotificationSettingsPageViewModel));