After saving metadata with ffmpeg:
1. Title change → rename the mp3 in place to "{01 - }?{sanitized title}.ext"
(same convention as the downloader uses)
2. Album-artist or album change → compute new {artistFirstPart}/{album}
directory, move the file there (create dirs as needed)
3. Old album dir is deleted if empty after the move; old artist dir
is deleted too if it also becomes empty
When only the album name changes (no artist change) the old in-place
folder-rename behaviour is preserved.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>