Replace hand-duplicated VIES/VAT-ID/PLZ/tracking logic with shared package

Deletes app/lib/vies.ts, vatId.ts, tracking.ts in favor of the newly unified @einfach-produktiv/invoicing modules — fixes the actual PLZ inconsistency (this repo already validated per-country digit counts; the backend hardcoded German-only) rather than just deduplicating code.

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

app/konto/bestellungen/[orderNumber]/page.tsx

@@ -9,7 +9,7 @@ import { formatPrice, formatDate } from "../../../lib/format";
 import { getSessionCustomer, getCustomerOrderDetail, customerOrderAction } from "../../../lib/customerAuth";
 import { getProductImagesByIds, getPaymentMethods, groupPaymentMethodsForCheckout, getMediaUrlById } from "../../../lib/payload";
 import { computeTaxBreakdown } from "@einfach-produktiv/invoicing";
-import { buildTrackingUrl, CARRIER_LABELS } from "../../../lib/tracking";
+import { buildTrackingUrl, CARRIER_LABELS, type Carrier } from "@einfach-produktiv/invoicing";
 import { OrderActionButton } from "./components/OrderActionButton";
 import { SwitchPaymentButton } from "./components/SwitchPaymentButton";
 import { OrderStatusBadge } from "../../components/OrderStatusBadge";
@@ -92,7 +92,7 @@ export default async function KontoBestellungDetailPage({ params }: { params: Pr
 
           {order.trackingNumber && (
             <div className="flex flex-col gap-1 w-full">
-              <p className="text-label text-text-muted">Sendungsverfolgung{order.carrier ? ` (${CARRIER_LABELS[order.carrier] ?? order.carrier})` : ""}</p>
+              <p className="text-label text-text-muted">Sendungsverfolgung{order.carrier ? ` (${CARRIER_LABELS[order.carrier as Carrier] ?? order.carrier})` : ""}</p>
               {(() => {
                 const trackingUrl = buildTrackingUrl(order.carrier, order.trackingNumber);
                 return trackingUrl ? (