Remove obsolete MissingFiles interface and its references:
- Delete core/missing_files.go and core/missing_files_test.go
- Remove RefreshAlbums method from AlbumRepository interface and implementation
- Remove RefreshAlbums tests from AlbumRepository test suite
- Update wire providers to use NewMaintenance instead of NewMissingFiles
- Update native API router to use Maintenance service
- Update missing.go handler to use Maintenance interface
All functionality is now consolidated in the core.Maintenance service.
Signed-off-by: Deluan <deluan@navidrome.org>