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.md

@@ -21,4 +21,5 @@ _Generated by `lib/commerce/conformance.sh`_
 | nettax | 11 | 0 | 11 |
 | stock | 19 | 0 | 19 |
 | refund | 20 | 0 | 20 |
-| **Total** | **278** | **0** | **278** |
+| integration | 19 | 0 | 19 |
+| **Total** | **297** | **0** | **297** |