Add bankName back to InvoiceSeller, shown alongside IBAN/BIC

Dropped by accident when bankDetails split into iban/bic — a bank name
has no fixed format to validate, so it stays free text, but it's still
useful context next to the account numbers in the invoice footer.

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

src/invoicePdf.tsx

@@ -340,7 +340,7 @@ export function InvoiceDocument({ order, seller }: { order: InvoiceOrder; seller
               reasons, e.g. a refund) — see this package's README. */}
           {(seller.iban || seller.bic) && (
             <Text style={{ marginTop: 4 }}>
-              Bankverbindung: {[seller.iban && `IBAN ${seller.iban}`, seller.bic && `BIC ${seller.bic}`].filter(Boolean).join(" · ")}
+              Bankverbindung: {[seller.bankName, seller.iban && `IBAN ${seller.iban}`, seller.bic && `BIC ${seller.bic}`].filter(Boolean).join(" · ")}
             </Text>
           )}
         </View>