Fix: Stornorechnung referenziert Originalnummer + Datum (§14 UStG Pflicht)

backend/routes/invoices.py

@@ -676,10 +676,18 @@ async def cancel_invoice(invoice_id: int, data: CancelBody, admin=Depends(requir
     invoice = _row_to_dict(row)
 
     # Storno-PDF: invoice-Dict als Stornobeleg aufbereiten
+    orig_date = (invoice.get("created_at") or "")[:10]
+    try:
+        from datetime import datetime as _dt
+        y, m, d = orig_date.split("-")
+        orig_date_de = f"{d}.{m}.{y}"
+    except Exception:
+        orig_date_de = orig_date
+
     storno_invoice = dict(invoice)
     storno_invoice["invoice_number"] = cancellation_number
     storno_invoice["notes"] = (
-        f"Stornierung zu Rechnung {invoice['invoice_number']}\n"
+        f"Stornorechnung zu Rechnung {invoice['invoice_number']} vom {orig_date_de}\n"
         f"Grund: {data.reason}"
     )
     storno_invoice["amount_net"]            = -invoice["amount_net"]