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/scoreboard.json

@@ -8,12 +8,13 @@
     "stack": {"pass": 16, "fail": 0},
     "quote": {"pass": 13, "fail": 0},
     "ledger": {"pass": 20, "fail": 0},
-    "order": {"pass": 21, "fail": 0},
+    "order": {"pass": 22, "fail": 0},
     "recon": {"pass": 20, "fail": 0},
     "federation": {"pass": 12, "fail": 0},
-    "attribution": {"pass": 16, "fail": 0}
+    "attribution": {"pass": 16, "fail": 0},
+    "payment": {"pass": 7, "fail": 0}
   },
-  "total_pass": 201,
+  "total_pass": 209,
   "total_fail": 0,
-  "total": 201
+  "total": 209
 }