ui: improve cover preview in edit metadata sheet and user changes

- Cover preview enlarged from 120x120 to 160x160 with shadow and better styling
- Layout changed from Wrap to Row with Expanded for side-by-side covers
- Label moved below image with labelMedium typography
- Cover editor section moved to top of edit form
- Added embedded cover preview cache with LRU eviction in metadata screen
- Added current cover extraction and preview in edit metadata sheet
- Added metadata sync to download history after edits
- Added embedded cover extraction cache in queue tab for downloaded items
- Added SAF mod-time tracking for cover refresh after metadata changes

go_backend/audio_metadata.go

@@ -911,9 +911,16 @@ func parseVorbisComments(data []byte, metadata *AudioMetadata) {
 			break
 		}
 
-		if commentLen > 10000 {
+		remaining := uint32(reader.Len())
+		if commentLen > remaining {
 			break
 		}
+		// Large comment entries are typically METADATA_BLOCK_PICTURE.
+		// Skip them so we can continue parsing normal text tags after/before.
+		if commentLen > 512*1024 {
+			reader.Seek(int64(commentLen), io.SeekCurrent)
+			continue
+		}
 
 		comment := make([]byte, commentLen)
 		if _, err := reader.Read(comment); err != nil {