fix(invoice): suppress GiroCode + payment terms for refunded (and paid) orders

User reported that fully refunded orders still rendered a SEPA GiroCode
QR asking the customer to wire the original total. The existing gate
("!viewModel.paid") only excluded literally-PAID orders; REFUNDED,
PARTIALLY_REFUNDED, VOIDED, AUTHORIZED, etc. all sneaked through and
produced a confusing payment request for an order whose outstanding
balance is in fact 0.

Root cause: the view model exposed two related but ambiguous flags
("paid" and "paymentStatus") and the renderer mixed them
inconsistently. Both the GiroCode generation step in
generateInvoice.server.tsx AND the GiroCode/payment-terms render gates
in InvoiceDocument.tsx checked the wrong one.

Fix: introduce a single derived "requiresPayment" flag on the view
model (composeInvoice.ts) that is true only when:
  - the document is a regular invoice (not a storno or an offer), AND
  - paymentStatus is neither "paid" nor "refunded".

That single flag now drives:
  - GiroCode QR generation (skip QR fetch for paid/refunded)
  - GiroCode block render in the PDF
  - payment-terms paragraph render in the PDF

The existing "Zahlstatus: Erstattet" / "Payment status: Refunded"
meta-row continues to communicate the refund visually — the change
just removes the contradictory call-to-pay.

Side benefits:
  - Storno (cancellation invoice) PDFs no longer emit the German
    "Bitte überweise …" payment-terms paragraph (kind=storno was
    falling through the same not-paid branch).
  - Same suppression for fully PAID orders (covered by a second smoke
    fixture) so the QR doesn't suggest re-payment after the fact.

Verification: new smoke fixtures (REFUNDED + PAID) build a real
GiroCode data URL and verify the PDF text neither contains the
"GiroCode" caption nor the "Bitte überweise" German payment terms,
while still showing the corresponding "Erstattet" / "Bezahlt" status
row. tsc / smoke / tests / build all green.

app/services/invoice/pdf/InvoiceDocument.tsx

@@ -446,7 +446,7 @@ export function InvoiceDocument({ invoice }: DocProps) {
           <Text style={[styles.paragraph, { marginTop: 16 }]}>
             {invoice.dueDate ? t.offerValidUntil(formatDate(invoice.dueDate, invoice.language)) : null}
           </Text>
-        ) : !invoice.paid && (
+        ) : invoice.requiresPayment && (
           <Text style={[styles.paragraph, { marginTop: 16 }]}>
             {invoice.dueDate
               ? t.paymentTerms(
@@ -457,7 +457,7 @@ export function InvoiceDocument({ invoice }: DocProps) {
           </Text>
         )}
 
-        {invoice.giroCodePngDataUrl && !invoice.paid && (
+        {invoice.giroCodePngDataUrl && invoice.requiresPayment && (
           <View style={styles.giroBlock}>
             <Image src={invoice.giroCodePngDataUrl} style={styles.giroImage} />
             <View>