Per-market pre-order logic — location-based inventory routing & per-market dispatch dates

1. **Location-based inventory for pre-order** — extend existing market→location logic so pre-order availability and inventory reads are scoped to the location assigned to that market. E.g. USA market reads only from US warehouse, ROW reads only from AU warehouse. 2. **Per-market dispatch dates** — allow different dispatch date messaging per market on the same product/variant simultaneously. E.g. USA shows "Estimated delivery: 1–10 May", ROW shows "Estimated delivery: 20–30 May".