Replace all SongGroup/SongArrangementGroup model usages with Label/SongArrangementLabel
after the schema migration to global labels. Updates 12 app files and 11 test files:
- SongService: createDefaultGroups now finds-or-creates global Labels by name
- ArrangementController: validates label_id (labels are global, no song-ownership)
- ProImportService: imports groups as Labels (firstOrCreate by name); does not
overwrite existing label colors per spec
- ProExportService/SongPdfController/TranslationService/etc: traverse via
arrangements -> arrangementLabels -> label -> songSlides chain
- All test factories and assertions adapted to label-based schema
- Fix probundle exports missing images (double slides/ prefix in storage path)
- Replace manual ZipArchive with PresentationBundle + ProBundleWriter from parser plugin
- Add per-agenda-item download route and buttons for songs and slide items
- Remove text layer from image-only slides in .pro generation
- Fix image conversion: upscale small images, black bars on 2 sides max (contain)
- Add upload warnings for non-16:9 and sub-1920x1080 images (German, non-blocking)
- Update SlideFactory and all tests to use slides/ prefix in stored_filename
- Add 11 new tests (agenda download, image conversion, upload warnings)
