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/pdf/InvoiceDocument.tsx

@@ -11,7 +11,7 @@ import {
 import React from "react";
 
 import { formatDate, formatMoney, formatQuantity, formatTaxRate } from "../format";
-import { getStrings } from "../i18n";
+import { getStrings, paymentStatusLabel as getPaymentStatusLabel } from "../i18n";
 import type { InvoiceLanguage } from "../i18n";
 import type { InvoiceViewModel, InvoiceLine, IssuerData, RecipientData } from "../types";
 
@@ -287,6 +287,22 @@ export function InvoiceDocument({ invoice }: DocProps) {
                   <Text style={styles.metaValue}>{invoice.recipientVatId}</Text>
                 </View>
               ) : null}
+              {invoice.kind === "invoice" && invoice.paymentGatewayNames.length > 0 && (
+                <View style={styles.metaRow}>
+                  <Text style={styles.metaLabel}>{t.paymentMethodLabel}</Text>
+                  <Text style={styles.metaValue}>
+                    {invoice.paymentGatewayNames.map(prettifyGatewayName).join(", ")}
+                  </Text>
+                </View>
+              )}
+              {invoice.kind === "invoice" && (
+                <View style={styles.metaRow}>
+                  <Text style={styles.metaLabel}>{t.paymentStatusLabel}</Text>
+                  <Text style={styles.metaValue}>
+                    {getPaymentStatusLabel(invoice.paymentStatus, t)}
+                  </Text>
+                </View>
+              )}
             </View>
           </View>
         </View>
@@ -545,3 +561,28 @@ function normaliseWebUrl(url: string): string {
   if (/^https?:\/\//i.test(trimmed)) return trimmed;
   return `https://${trimmed.replace(/^\/\//, "")}`;
 }
+
+/**
+ * Turn a Shopify payment-gateway machine name (e.g. `shopify_payments`,
+ * `manual`, `bogus`) into something a customer can read on the invoice. We
+ * keep this purely cosmetic — the underlying value is preserved for any
+ * downstream automation.
+ */
+function prettifyGatewayName(name: string): string {
+  const known: Record<string, string> = {
+    manual: "Manual",
+    bogus: "Bogus (Test)",
+    shopify_payments: "Shopify Payments",
+    paypal: "PayPal",
+    cash_on_delivery: "Cash on delivery",
+    "cash-on-delivery": "Cash on delivery",
+  };
+  const key = name.trim().toLowerCase();
+  if (known[key]) return known[key];
+  // Replace separators and title-case each word.
+  return key
+    .split(/[_\s-]+/)
+    .filter(Boolean)
+    .map((w) => w.charAt(0).toUpperCase() + w.slice(1))
+    .join(" ");
+}