One file per use case under the feature folder (Tracks/PlayLists/Users),
dropping the Commands/Queries/Handlers sub-folders and their namespaces.
Each file now holds the record and its handler in namespace
Musify.Application.<Feature>; external usings updated accordingly.
Build: 0 warnings, 0 errors.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
