The GOA shop e2e path used to walk every product template every run, which
was slow and often hit balance or time budgets after the first few pays.
Keep the full catalog in E2E_SHOP_PRODUCTS (id|name|amount, synced with the
merchant landing). Each e2e run shuffles that list and pays only
E2E_SHOP_PICK_N products (default 2). Shop pays pin instance goa-shop for
public template POSTs; settlement payto matches the landing shop popup.
Docs in README.md and TESTS.md describe the pick behaviour and env overrides.
