v3.18.38 — Fix: MoMo GA4 revenue value

showMomoConfirmation()'s purchase event was missing the value field, recording all MoMo orders as zero revenue in GA4 — not a data problem, a structural one: the function never had lexical access to the order total captured earlier in dd_place_order's closure. Now captured at MoMo-initiation time (currentOrderTotal) and threaded through. Trustworthy by construction: MTN's USSD approval flow only allows accept/reject at the exact quoted amount, so the initiation-time total is guaranteed to equal the confirmed-paid amount. See RELEASE.md.