Export Bulk Intake

Export all scored claims in a bulk-intake batch in a single call.

Complements the per-claim export (POST /claims/{id}/export/{format}): rather than one call per claim, this returns every claim in the batch as a single csv (one row per claim) or json document, keyed by the caller's external_id. This is the deliverable for a "send me N real claims" proof — one spreadsheet to diff Zicron scores against the partner's own reviewers.

Read-only; aggregates data that already exists (no new inference, no new storage). Returns 404 for unknown batch IDs.