commerce: provider-neutral payment-request envelope (8 tests) — Phase 5 ext

payment.sx — payment-request materialises {:order :amount :currency :return-url}
at the IO edge (amount from the ledger, currency/return-url host-supplied), so
lib/commerce stays vendor-agnostic; SumUp/Stripe adapters live in the orders
service and order-settle!(ref, amount) is the resume seam. pending-payments
enumerates suspended orders + envelopes (host poller seam). Gotcha handled: a
Scheme string flow-payload round-trips back wrapped as {:scm-string ...} —
unwrapped via scm->string. Total 209/209 across 13 suites.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/commerce/conformance.sh

@@ -17,7 +17,7 @@ if [ ! -x "$SX_SERVER" ]; then
   exit 1
 fi
 
-SUITES=(catalog cart price api promo stack quote ledger order recon federation attribution)
+SUITES=(catalog cart price api promo stack quote ledger order recon federation attribution payment)
 
 OUT_JSON="lib/commerce/scoreboard.json"
 OUT_MD="lib/commerce/scoreboard.md"
@@ -68,6 +68,7 @@ run_suite() {
 (load "lib/commerce/quote.sx")
 (load "lib/commerce/ledger.sx")
 (load "lib/commerce/order.sx")
+(load "lib/commerce/payment.sx")
 (load "lib/commerce/recon.sx")
 (load "lib/commerce/federation.sx")
 (load "lib/commerce/attribution.sx")