commerce: end-to-end composition integration suite (19 tests) — hardening

tests/integration.sx — one narrative across every module: catalog -> stock
check -> quote (promo+stack+tax) -> attribution -> order flow -> payment
envelope -> settle -> recon -> refund flow -> ledger mismatch, asserting the
seams tie together with consistent numbers. Proves the three-substrate
composition (minikanren pricing + flow lifecycle + persist ledger) end to end.
Total 297/297 across 18 suites.

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

lib/commerce/scoreboard.json

@@ -16,9 +16,10 @@
     "window": {"pass": 19, "fail": 0},
     "nettax": {"pass": 11, "fail": 0},
     "stock": {"pass": 19, "fail": 0},
-    "refund": {"pass": 20, "fail": 0}
+    "refund": {"pass": 20, "fail": 0},
+    "integration": {"pass": 19, "fail": 0}
   },
-  "total_pass": 278,
+  "total_pass": 297,
   "total_fail": 0,
-  "total": 278
+  "total": 297
 }