Wayfinder: chart the Shopify headless commerce map

The route from "mozimo.in displays Shopify products" to "mozimo.in sells them",
as a plan with a phase spine and gates, plus the open decision tickets that
still shape it and the evidence they rest on.

- .scratch/shopify-headless-commerce/: plan.md (phases and gates), map.md (the
  wayfinder map), 10 open decision tickets
- CONTEXT.md: Storefront / Theme store / Cart / Parity vocabulary
- docs/adr/0001-0003: Checkout stays Shopify-hosted, one Variant per product,
  the checkout domain stays shop.mozimo.in
- docs/research/ and docs/shopify-catalog-inventory.md: verified store facts,
  the Cart API probe, and the catalogue inventory

Raw Shopify doc scrapes under .scratch/shopify-research/ are ignored: they are
working material, not record.

CONTEXT.md

@@ -0,0 +1,43 @@
+# Mozimo Commerce
+
+The commerce domain for mozimo.in: a headless Storefront reading from Shopify, migrating off a classic Shopify theme store.
+
+## Language
+
+### Surfaces
+
+**Storefront**:
+The headless commerce application in this repository, serving mozimo.in.
+_Avoid_: Site, website, app
+
+**Theme store**:
+The classic Shopify theme storefront at shop.mozimo.in, retained only until the Storefront reaches Parity.
+_Avoid_: Old site, live shop, Shopify site
+
+**Checkout**:
+The Shopify-hosted checkout a buyer is handed off to when they finish with their Cart. It is never rendered by the Storefront.
+_Avoid_: Our checkout, custom checkout, payment page
+
+### Catalog
+
+**Shopify catalog**:
+The products held in the Shopify store: the commerce truth for what can be bought, at what price, and whether it is available.
+_Avoid_: Product database, real catalog
+
+**Editorial catalog**:
+The hand-curated product data in `src/data/catalog.ts`, used to place products into merchandising slots on the Storefront. Not commerce truth.
+_Avoid_: Catalog, products file
+
+**Variant**:
+A product's purchasable unit, identified by a Shopify variant ID. Every product in the Shopify catalog currently has exactly one Variant, and sizes are modelled as separate products rather than as options.
+_Avoid_: SKU, option, size
+
+### Commerce
+
+**Cart**:
+The Shopify cart object holding a buyer's intended purchase, identified by a Shopify cart ID. The header's "Bag" label refers to the Cart.
+_Avoid_: Bag, basket, trolley
+
+**Parity**:
+The set of commercial capabilities the Storefront must have before the Theme store can be retired.
+_Avoid_: Feature complete, launch-ready