feat(invoice): informal German tone + show payment method and status

- i18n.de: switch Sie/Ihren to du/dein for salutation, thank-you line,
  customer-VAT label and payment-terms paragraph. Closing line was
  already informal.
- i18n: add paymentMethodLabel/paymentStatusLabel + per-status labels
  (paid/unpaid/partial/refunded) for both DE and EN, plus
  derivePaymentStatus helper that condenses Shopify's
  displayFinancialStatus (PAID, PARTIALLY_PAID, REFUNDED, …) into a
  4-value enum.
- loadOrderForInvoice: query Order.paymentGatewayNames and propagate it
  on the raw view-model.
- composeInvoice + types: expose paymentStatus + paymentGatewayNames on
  InvoiceViewModel (filtered/trimmed). loadDraftOrderForOffer keeps
  paymentGatewayNames empty (drafts have no gateway yet).
- InvoiceDocument: render two new meta rows on real invoices —
  'Zahlart / Payment method' (joined, prettified gateway names) and
  'Zahlstatus / Payment status' (translated label). Storno + offer kinds
  intentionally omit them.
- scripts/render-sample.ts: extend smoke checks to assert the informal
  DE wording, the new payment-method/status rows and the
  paymentStatus/paymentGatewayNames composer outputs.

app/services/invoice/composeInvoice.ts

@@ -11,7 +11,7 @@ import type {
   VatBreakdownEntry,
 } from "./types";
 import { addDays } from "./format";
-import { pickLanguage, type InvoiceLanguage } from "./i18n";
+import { derivePaymentStatus, pickLanguage, type InvoiceLanguage } from "./i18n";
 
 interface ComposeArgs {
   order: RawOrderForInvoice;
@@ -69,6 +69,10 @@ export function composeInvoice({
       : undefined;
 
   const paid = (order.displayFinancialStatus || "").toUpperCase() === "PAID";
+  const paymentStatus = derivePaymentStatus(order.displayFinancialStatus);
+  const paymentGatewayNames = (order.paymentGatewayNames ?? []).filter(
+    (n) => typeof n === "string" && n.trim().length > 0,
+  );
 
   if (storno) {
     lines = lines.map((l) => ({
@@ -107,6 +111,8 @@ export function composeInvoice({
     totals,
     notices,
     paid,
+    paymentStatus,
+    paymentGatewayNames,
   };
 }