feat(ocr): discard abandoned capture batches

A bad scan, the wrong PDFs or a duplicate upload used to leave a batch
sitting in READY_FOR_REVIEW forever, because the only exits were confirm
(posts to the books) or rejecting every page one at a time. Add a
DISCARDED terminal status to both OCR domains and a single endpoint per
domain that rejects every page still pending in one shot.

Discarding is refused once anything has landed: statements once a page is
POSTED, policies once a page is APPLIED. Those batches did real work and
have to be settled page by page.

- POST /statements/batches/:id/discard
- POST /policy-ocr/batches/:id/discard
- shared DiscardBatchCard on both review screens, gated the same way

packages/database/prisma/schema.prisma

@@ -399,6 +399,10 @@ enum PolicyOcrBatchStatus {
   READY_FOR_REVIEW
   COMPLETED
   FAILED
+  /// Abandoned by staff before anything was applied — a bad scan, the wrong
+  /// PDFs, a duplicate upload. Distinct from COMPLETED so the queue can tell
+  /// "we did the work" from "we threw it away".
+  DISCARDED
 }
 
 /// One parsed policy page — one Policy → one Customer (after staff confirms).
@@ -573,6 +577,10 @@ enum StatementBatchStatus {
   READY_FOR_REVIEW
   COMPLETED
   FAILED
+  /// Abandoned by staff before anything was posted — a bad scan, the wrong
+  /// PDFs, a duplicate upload. Distinct from COMPLETED so the queue can tell
+  /// "we did the work" from "we threw it away".
+  DISCARDED
 }
 
 enum StatementDocumentStatus {