feat(recibos): split a receipt, sin fondos per receipt, keep a batch open

Three asks from the 2026-10-08 meeting, all on the OCR receipt queue.

- Split: one receipt paid by several customers (411 + 523 sharing water
  3014057) posts one charge per part. statement_document_splits holds free
  amounts that must sum to the receipt in cents, checked on save and again
  at confirm; "partes iguales" fills them in. Each part's row carries
  captureRef <docId>#<n>, so the double-post guard still holds.
- Sin fondos per receipt: StatementDocument.outstanding, toggled in review.
  At confirm a line is outstanding if its receipt or the whole check is.
- Open batch: POST /statements/batches/:id/files appends scans, numbered
  after the existing pages; a COMPLETED batch reopens. The confirm card
  prefills the check the batch was last posted against.

Verified on dev against a real batch: 1,892.00 split 946/946 across two
customers, a sibling receipt posted outstanding, second confirm refused.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/api/src/statements/statements.controller.ts

@@ -4,6 +4,7 @@ import {
   Get,
   Param,
   Patch,
+  Put,
   Post,
   Query,
   Req,
@@ -22,7 +23,7 @@ import { RequireAbility } from "../auth/require-ability.decorator";
 import { AuditService } from "../common/audit.service";
 import type { UploadedFileLike } from "../storage/upload-file";
 import { StatementsService } from "./statements.service";
-import { ConfirmBatchDto, ReviewDocumentDto } from "./statement.dto";
+import { ConfirmBatchDto, ReviewDocumentDto, SetSplitsDto } from "./statement.dto";
 
 /**
  * Statement OCR intake (RECEIPT_CAPTURE_SPEC §2).
@@ -117,6 +118,39 @@ export class StatementsController {
     return batch;
   }
 
+  /** More scans for a batch kept open for one check. */
+  @Post("batches/:id/files")
+  @RequireAbility("statement:ingest")
+  @UseInterceptors(FilesInterceptor("files", 25, { limits: { fileSize: 50 * 1024 * 1024 } }))
+  async addFiles(
+    @Param("id") id: string,
+    @UploadedFiles() files: UploadedFileLike[] | undefined,
+    @Req() req: Request,
+  ) {
+    const batch = await this.statements.addFiles(id, files ?? []);
+    void this.audit.log(this.actingId(req), "statement.batch.add-files", {
+      batchId: id,
+      added: files?.length ?? 0,
+    });
+    return batch;
+  }
+
+  /** Split one receipt across several customers; empty parts undo it. */
+  @Put("documents/:id/splits")
+  @RequireAbility("statement:review")
+  async setSplits(
+    @Param("id") id: string,
+    @Body() dto: SetSplitsDto,
+    @Req() req: Request,
+  ) {
+    const doc = await this.statements.setSplits(id, dto.parts, this.actingId(req));
+    void this.audit.log(this.actingId(req), "statement.document.split", {
+      documentId: id,
+      parts: dto.parts.length,
+    });
+    return doc;
+  }
+
   @Patch("documents/:id")
   @RequireAbility("statement:review")
   async review(