- Added routes in router.go: POST, GET, PUT, DELETE /playlists/:id/collaborators
- Applied RequireOwnershipOrAdmin middleware to POST, PUT, DELETE routes
- GET route accessible to collaborators (service layer checks permissions)
- Fixed UpdateCollaboratorPermission handler to use RespondWithAppError
- All handlers already existed in playlist_handler.go
- All endpoints properly authenticated and ownership checks enforced
Phase: PHASE-1
Priority: P0
Progress: 5/267 (1.9%)
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