Add configurable shuffle depth for copy order

ShuffleDepth in DiskProfile controls how files are selected:
  -1 = no shuffle (preserve source order)
   0 = all files in random order
   N = group files by folder at depth N from /media, shuffle groups,
       copy entire group before moving to next

Exposed in disk profile UI as a select with level descriptions.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/api/handlers_copy.go

@@ -26,6 +26,7 @@ func (s *Server) copyOptions(cfg *config.Config, diskInfo disk.DiskInfo, overwri
 		opts.ReserveFreeGB = p.ReserveFreeGB
 		opts.FileSelectMode = config.FileSelectMode(p.FileSelectMode)
 		opts.Transcode = p.Transcode
+		opts.ShuffleDepth = p.ShuffleDepth
 	} else {
 		opts.DestFolder = cfg.DestFolder
 		opts.ReserveFreeGB = cfg.ReserveFreeGB