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/loadOrderForInvoice.server.ts

@@ -12,6 +12,7 @@ export interface RawOrderForInvoice {
   processedAt: string | null;
   currencyCode: string;
   displayFinancialStatus: string | null;
+  paymentGatewayNames: string[];
   customer: {
     firstName: string | null;
     lastName: string | null;
@@ -77,6 +78,7 @@ const QUERY = `#graphql
       processedAt
       currencyCode
       displayFinancialStatus
+      paymentGatewayNames
       taxesIncluded
       customer {
         firstName
@@ -161,6 +163,7 @@ interface RawAdminResponse {
       processedAt: string | null;
       currencyCode: string;
       displayFinancialStatus: string | null;
+      paymentGatewayNames: string[] | null;
       taxesIncluded: boolean;
       customer: {
         firstName: string | null;
@@ -213,6 +216,7 @@ export async function loadOrderForInvoice(
     processedAt: order.processedAt,
     currencyCode: order.currencyCode,
     displayFinancialStatus: order.displayFinancialStatus,
+    paymentGatewayNames: order.paymentGatewayNames ?? [],
     taxesIncluded: order.taxesIncluded,
     customer: order.customer,
     billingAddress: order.billingAddress,