Add optional per-line SKU + shipping recipient company/contact fields (v0.2.7)

Invoice PDFs (visual + EN16931 XML) and correction invoices now show an
"Art.-Nr." line when an order item has a SKU snapshot, and the
Lieferadresse block includes company name/contact email/phone when set.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@einfach-produktiv/invoicing",
-  "version": "0.2.6",
+  "version": "0.2.7",
   "private": true,
   "description": "Shared invoice / correction-invoice (Stornorechnung, Gutschrift) PDF generation and VAT-breakdown math, consumed as a git dependency by both the einfach-produktiv frontend and the payload backend — not published to npm.",
   "type": "module",