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/Abstract/FolderCustomizationPageAbstract.cs

@@ -0,0 +1,6 @@
+using Wino.Mail.WinUI;
+using Wino.Mail.ViewModels;
+
+namespace Wino.Views.Abstract;
+
+public abstract class FolderCustomizationPageAbstract : BasePage<FolderCustomizationPageViewModel> { }