Retrieve previously generated procedure recommendations for a skin analysis batch.

Reachable by vendor dashboard sessions AND by widget sessions (X-Channel: widget),
which authenticate as vendor staff. Either way the batch is vendor-scoped from the
scan row itself: a batch belonging to another vendor returns 403, never an empty list.

Recommendations exist only for vendors an Oyster admin has granted procedure
recommendations. Generation runs in a background job when the scan completes, so a
read immediately after a scan may legitimately return an empty data array while
that job is still running — clients should follow the procedure_generation frames
on the scan's routine_progress_realtime channel rather than polling.

Rows carry source and is_vendor_offering. Customer-facing surfaces must render
only is_vendor_offering: true entries: a global row is guidance from Oyster's
reference catalogue, not a treatment the clinic has said it performs.