Batch operations

POST /v1/{usecase}/batch accepts 1-100 items as one job (24-hour ceiling) and charges price multiplied by the number of items. GET /v1/{usecase}/batch/{job_id} returns per-item counts, a presigned result_url and, when the file is 1 MB or smaller, the results inline as result_data. A batch is refused as a whole, before any credit is reserved, when one item names a registry Delpha cannot query (422 unsupported_registry, naming the offending item). Settlement is partial: when the job completes, only the items that succeeded are charged and the rest of the reservation is refunded.