When Navidrome has a Japanese path in its DB but the file was saved with
a romaji filename by the download pipeline, the existing fallback chain
compared the Japanese title stem against romaji filenames and always
failed. Added _findFileByStemOrRomaji which converts the stem via
romajiForStorage before the final recursive search, covering all three
endpoints: edit-metadata, delete-song, song-sorttags.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>