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.Core.Domain/Enums/WinoPage.cs

@@ -12,6 +12,7 @@ public enum WinoPage
     ContactsPage,
     MailRenderingPage,
     AccountDetailsPage,
+    FolderCustomizationPage,
     MergedAccountDetailsPage,
     ManageAccountsPage,
     AccountManagementPage,