Fix CII schema violation: emit an empty ApplicableHeaderTradeDelivery element

Mustang's Phase 4 CI check (validate-einvoice.yml) caught this on its very first real run: @e-invoice-eu/core's UBL->CII conversion silently drops the whole Delivery container when cac:Delivery is absent from the UBL input, breaking CII's fixed Agreement/Delivery/Settlement element order and failing schema validation on every generated e-invoice (original, Storno, and Gutschrift alike).

src/einvoice/buildEInvoiceData.ts

@@ -69,6 +69,19 @@ function isoDate(iso: string): string {
   return iso.slice(0, 10);
 }
 
+// Empty on purpose — this shop doesn't track a separate delivery date/
+// location distinct from the invoice itself (and a Storno never shipped at
+// all, so asserting one would be factually wrong). The *element* still has
+// to exist, though: CII's SupplyChainTradeTransaction is a fixed
+// Agreement/Delivery/Settlement sequence, and @e-invoice-eu/core's UBL→CII
+// conversion drops the whole `ram:ApplicableHeaderTradeDelivery` container
+// when `cac:Delivery` is absent from the UBL input — which then fails
+// schema validation (Mustang: "Invalid content ... ApplicableHeaderTrade
+// Settlement. One of ApplicableHeaderTradeDelivery is expected", caught by
+// the Phase 4 CI check on the very first real run). An empty object here
+// still emits the required empty `<ram:ApplicableHeaderTradeDelivery/>`.
+const DELIVERY: UblInvoice["cac:Delivery"] = {};
+
 function paymentMeans(seller: InvoiceSeller, paymentMethodTitle: string): UblInvoice["cac:PaymentMeans"] {
   if (!seller.iban) return undefined;
   return [
@@ -180,6 +193,7 @@ export function buildEInvoiceData(order: InvoiceOrder, seller: InvoiceSeller): I
         order.city,
         order.country,
       ),
+      "cac:Delivery": DELIVERY,
       "cac:PaymentMeans": paymentMeans(seller, order.paymentMethodTitle),
       "cac:TaxTotal": taxTotal(rateGroups),
       "cac:LegalMonetaryTotal": {
@@ -243,6 +257,7 @@ export function buildCorrectionEInvoiceData(kind: CorrectionInvoiceKind, order:
         order.city,
         order.country,
       ),
+      "cac:Delivery": DELIVERY,
       "cac:PaymentMeans": paymentMeans(seller, "Überweisung"),
       "cac:TaxTotal": taxTotal(rateGroups),
       "cac:LegalMonetaryTotal": {