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/disk/profile.go

@@ -12,6 +12,8 @@ type DiskProfile struct {
 	FileSelectMode string  `json:"file_select_mode"`
 	ReserveFreeGB  float64 `json:"reserve_free_gb"`
 	AutoCopy       bool    `json:"auto_copy"`
+	// ShuffleDepth: -1=выкл, 0=файлы вразнобой, 1+=папки на глубине N от корня /media
+	ShuffleDepth int `json:"shuffle_depth"`
 
 	// nil = не транскодировать видео
 	Transcode *TranscodeProfile `json:"transcode,omitempty"`
@@ -66,5 +68,6 @@ func DefaultProfile() *DiskProfile {
 		FileSelectMode: "new",
 		ReserveFreeGB:  2.0,
 		AutoCopy:       false,
+		ShuffleDepth:   -1,
 	}
 }