feat(invoice): show refund + outstanding-amount rows on the PDF

When a Shopify order has been (partially or fully) refunded the PDF
now mirrors the order-page totals block:

  Gesamtbetrag brutto      629,95 EUR
  Zurückerstattet         -629,95 EUR
  Offener Betrag             0,00 EUR

So the customer immediately sees that nothing is owed any more, even
though the original invoice gross stays unchanged for tax-document
correctness (the refund is itemised as a separate row, not subtracted
from the line totals).

Plumbing:

  - GraphQL: added `totalRefundedSet` to OrderForInvoice query.
  - RawOrderForInvoice: new optional `totalRefundedSet` field
    (null for drafts/offers — they never have refunds).
  - InvoiceViewModel: new `refundedAmount: number` (gross, in the
    same currency as `totals.gross`). Always present, 0 for storno
    and offer documents and for non-refunded invoices.
  - composeInvoice parses the gross refund out of `totalRefundedSet`
    (defensive parseFloat, clamped to >= 0).
  - InvoiceDocument renders the two extra rows under `grossTotal`
    only when `refundedAmount > 0`. Uses the existing total-row
    styles for visual consistency.
  - i18n: added `refundedLabel` ("Zurückerstattet" / "Refunded") and
    `outstandingLabel` ("Offener Betrag" / "Outstanding amount") to
    both languages.

Verification: render-sample fixture now mirrors the full gross as
refunded and asserts the PDF text contains "Zurückerstattet",
"Offener Betrag", and "0,00 EUR" as the final outstanding row, on
top of the previous suppressions (no GiroCode, no payment terms).
tsc / smoke / tests / build all green.

app/services/invoice/loadDraftOrderForOffer.server.ts

@@ -172,6 +172,8 @@ export async function loadDraftOrderForOffer(
     subtotalSet: draft.subtotalPriceSet,
     totalTaxSet: draft.totalTaxSet,
     totalPriceSet: draft.totalPriceSet,
+    // Drafts have no concept of refunds.
+    totalRefundedSet: null,
     taxLines: draft.taxLines || [],
     lineItems: (draft.lineItems?.edges || []).map((e) => {
       const node = e.node;