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/Helpers/XamlHelpers.cs

@@ -274,6 +274,10 @@ public static class XamlHelpers
         };
     }
 
+    // Segoe Fluent icon glyphs for the show/hide toggle on the folder
+    // customization page. E7B3 = "Hide" (eye with slash), E7B2 = "RedEye".
+    public static string GetHideGlyph(bool isHidden) => isHidden ? "\uE7B3" : "\uE7B2";
+
     public static WinoIconGlyph GetSpecialFolderPathIconGeometry(SpecialFolderType specialFolderType)
     {
         return specialFolderType switch