Preview invoice bundle lines

Resolves bundle child lines for a product with metadata.invoiceBundle using the same resolver and expand rules as replaceInvoice when that invoice rebuild runs for an anchor. Pass anchorLineQuantity when bundle steps use quantityScale anchor_line_quantity so preview matches the extend-occupation / period main line. When the anchor is Extend occupation period, pass terrainId so ICY meter steps match that terrain, and invoiceBillingAnchorEndDateIso (anchor endDate) when steps use extendAccessMethod. Pass invoiceItemsForBillOnceContext and anchorItemListIndex together so steps with billOncePerInvoice behave like replaceInvoice (shared steps only under the first eligible anchor in array order). Optional existingAnchorSnapshots aligns regenerate detection with the last-loaded invoice for preview.