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- DB: stems table with trackId FK, fileKey, sortOrder, createdById - API: GET/POST/DELETE stems, presigned upload URL, ZIP download via fflate - Web: StemUploadDropzone (multi-file, batch upload, progress bars) - Web: StemList with download-all-ZIP and per-stem delete - Web: STEMs tab in track detail view - Icon: add 'music' icon to inline set - Auto-migration runs stems table creation on boot Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>