feat(eims): printable receipt PDF with RRN and QR

eims-receipt-document.mapper.ts maps an EimsReceipt onto the shared
InvoiceDocumentModel layout, reading amounts back out of the stored request
body. Refuses to render anything not REGISTERED. GET
invoices/:id/eims/receipts/:receiptId/document, scoped to the invoice.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/edr-freight-api/src/modules/billing/documents/invoice-document.service.ts

@@ -18,6 +18,15 @@ import {
 
 export type InvoiceDocumentKind = "INVOICE" | "RECEIPT";
 
+/**
+ * MoR returns `signedQR`/`qr` as a base64 PNG already rendered server-side — confirmed against the
+ * Postman collection's `register` response (`signedQR` decodes to a PNG magic-byte header), not a
+ * payload we encode ourselves. Wrap, don't encode. Shared by `Invoice.eimsSignedQr`
+ * (`BillingService`) and `EimsReceipt.qr` (`eims-receipt-document.mapper.ts`) — same convention,
+ * same gateway.
+ */
+export const pngDataUrl = (base64: string): string => `data:image/png;base64,${base64}`;
+
 /** One billed line on the document (charge type / fee type agnostic). */
 export interface InvoiceDocumentLine {
   description: string | null;