Matching has always been by relative path, so any folder layout works as
long as both libraries use the same one. Remove the depth and loose-root-file
warnings, which flagged valid layouts, and reword the UI and README to say
"same folder layout on both sides" with Artist/Album/Title.ext only as an
example. The "elsewhere" fallback is now described as same top-level folder,
different subfolder. Add a test covering flat and deeply nested layouts.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>