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/Entities/Mail/MailItemFolder.cs

@@ -24,6 +24,11 @@ public class MailItemFolder : IMailItemFolder
     public bool IsSynchronizationEnabled { get; set; }
     public bool IsHidden { get; set; }
     public bool ShowUnreadCount { get; set; }
+
+    // User-defined ordering within its navigation section (Pinned / Categories / More).
+    // 0 means "no custom order set" — the folder falls back to the default sort
+    // (alphabetic for More, canonical SpecialFolderType order as a tiebreak for Pinned).
+    public int Order { get; set; }
     public DateTime? LastSynchronizedDate { get; set; }
 
     // For IMAP