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/i18n.ts

@@ -52,6 +52,44 @@ export interface InvoiceStrings {
   webLabel: string;
   phoneLabel: string;
   paidStamp: string;
+  paymentMethodLabel: string;
+  paymentStatusLabel: string;
+  paymentStatusPaid: string;
+  paymentStatusUnpaid: string;
+  paymentStatusPartial: string;
+  paymentStatusRefunded: string;
+}
+
+/** Status displayed for the order's payment, derived from Shopify's
+ *  `displayFinancialStatus`. */
+export type PaymentStatus = "paid" | "unpaid" | "partial" | "refunded";
+
+export function paymentStatusLabel(
+  status: PaymentStatus,
+  strings: InvoiceStrings,
+): string {
+  switch (status) {
+    case "paid":
+      return strings.paymentStatusPaid;
+    case "partial":
+      return strings.paymentStatusPartial;
+    case "refunded":
+      return strings.paymentStatusRefunded;
+    default:
+      return strings.paymentStatusUnpaid;
+  }
+}
+
+/** Maps Shopify's `displayFinancialStatus` to our condensed enum. Values not
+ *  signalling actual receipt of money map to "unpaid". */
+export function derivePaymentStatus(
+  displayFinancialStatus: string | null | undefined,
+): PaymentStatus {
+  const v = (displayFinancialStatus || "").toUpperCase();
+  if (v === "PAID") return "paid";
+  if (v === "PARTIALLY_PAID") return "partial";
+  if (v === "REFUNDED" || v === "PARTIALLY_REFUNDED") return "refunded";
+  return "unpaid";
 }
 
 const de: InvoiceStrings = {
@@ -65,7 +103,7 @@ const de: InvoiceStrings = {
   invoiceNumber: "Rechnungs-Nr.",
   invoiceDate: "Rechnungsdatum",
   deliveryDate: "Lieferdatum",
-  customerVatId: "Ihre USt-Id.",
+  customerVatId: "Deine USt-Id.",
   position: "Pos.",
   description: "Beschreibung",
   quantity: "Menge",
@@ -74,12 +112,12 @@ const de: InvoiceStrings = {
   netTotal: "Gesamtbetrag netto",
   vatLine: (r) => `zzgl. Umsatzsteuer ${r}`,
   grossTotal: "Gesamtbetrag brutto",
-  salutationGeneric: "Sehr geehrte Damen und Herren,",
+  salutationGeneric: "Hallo,",
   thankYouLine:
-    "vielen Dank für Ihren Auftrag. Wir erlauben uns, Ihnen folgende Leistungen in Rechnung zu stellen:",
+    "vielen Dank für deine Bestellung. Wir berechnen dir folgende Leistungen:",
   closing: "Danke für deinen Einkauf",
   paymentTerms: (days, due) =>
-    `Bitte überweisen Sie den Rechnungsbetrag innerhalb von ${days} Tagen, spätestens bis zum ${due}, auf das unten angegebene Konto. Bei Fragen zur Rechnung stehen wir Ihnen gerne zur Verfügung.`,
+    `Bitte überweise den Rechnungsbetrag innerhalb von ${days} Tagen, spätestens bis zum ${due}, auf das unten angegebene Konto. Bei Fragen zur Rechnung sind wir gerne für dich da.`,
   paymentTermsImmediate:
     "Der Rechnungsbetrag ist sofort nach Erhalt zur Zahlung fällig.",
   giroCodeCaption: "GiroCode",
@@ -109,6 +147,12 @@ const de: InvoiceStrings = {
   webLabel: "Web",
   phoneLabel: "Tel.",
   paidStamp: "BEZAHLT",
+  paymentMethodLabel: "Zahlart",
+  paymentStatusLabel: "Zahlstatus",
+  paymentStatusPaid: "Bezahlt",
+  paymentStatusUnpaid: "Offen",
+  paymentStatusPartial: "Teilweise bezahlt",
+  paymentStatusRefunded: "Erstattet",
 };
 
 const en: InvoiceStrings = {
@@ -165,6 +209,12 @@ const en: InvoiceStrings = {
   webLabel: "Web",
   phoneLabel: "Tel.",
   paidStamp: "PAID",
+  paymentMethodLabel: "Payment method",
+  paymentStatusLabel: "Payment status",
+  paymentStatusPaid: "Paid",
+  paymentStatusUnpaid: "Outstanding",
+  paymentStatusPartial: "Partially paid",
+  paymentStatusRefunded: "Refunded",
 };
 
 // Locale → invoice language. We only render in German (`de`) when the