Get Bulk Intake Status

Poll the status of a bulk intake batch.

Complements the bulk_intake.completed webhook (and is the fallback when no webhook_url was provided): partners can poll the batch_id returned by POST /intake/bulk until status is terminal.

Item shape matches the webhook's items array exactly, so partners can share one parser for both paths.

Returns 404 for unknown batch IDs and for batches submitted with async_scoring=false (no background work exists to poll — the sync response was already final).