Blog categories (hasMany), shipping-address contact fields, product SKU on invoices

- Posts.categories is now hasMany — blog list/detail/live-preview render
  a comma-joined list instead of a single category.
- Checkout's "Abweichende Lieferadresse" gains optional Firma + Kontakt-
  E-Mail/Telefon fields (handed to the shipping carrier, not used for
  customer communication).
- Customer profile can now store its own shipping address (mirroring
  Customers.ts's new "Lieferadresse" tab), prefilling the checkout
  override instead of always starting blank.
- Product-level optional SKU (previously only on variants) snapshots onto
  each order item and shows up on invoices (visual + EN16931 XML),
  the confirmation email, and the account order detail page.

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

@@ -120,6 +120,7 @@ export default async function KontoBestellungDetailPage({ params }: { params: Pr
           {order.hasDifferentShippingAddress && (
             <div className="flex flex-col gap-1 w-full">
               <p className="text-label text-text-muted">Lieferadresse</p>
+              {order.shippingCompanyName && <p className="text-body-sm text-text-primary">{order.shippingCompanyName}</p>}
               <p className="text-body-sm text-text-primary">
                 {order.shippingFirstName} {order.shippingLastName}
               </p>
@@ -127,6 +128,11 @@ export default async function KontoBestellungDetailPage({ params }: { params: Pr
               <p className="text-body-sm text-text-primary">
                 {order.shippingZip} {order.shippingCity}, {order.shippingCountry}
               </p>
+              {(order.shippingContactEmail || order.shippingContactPhone) && (
+                <p className="text-body-sm text-text-muted">
+                  {[order.shippingContactEmail, order.shippingContactPhone].filter(Boolean).join(" · ")}
+                </p>
+              )}
             </div>
           )}
 
@@ -145,6 +151,7 @@ export default async function KontoBestellungDetailPage({ params }: { params: Pr
                   </p>
                   {!order.kleinunternehmer && <p className="text-label text-text-muted">inkl. {item.taxRatePercent}% MwSt.</p>}
                   {item.bundleContents && <p className="text-label text-text-muted">{item.bundleContents}</p>}
+                  {item.sku && <p className="text-label text-text-muted">Art.-Nr. {item.sku}</p>}
                   {item.returnQuantity > 0 && (
                     <p className="text-label text-text-muted">davon {item.returnQuantity} zurückgesendet</p>
                   )}