commerce: catalog facts + multidirectional relations + conformance harness (16 tests)

catalog.sx — catalog snapshot (products/variants/stock as fact tuples),
relational accessors (producto/varianto/stocko, derived priceo/classo/
unit-priceo) usable forward and backward, deterministic catalog-price/
-class/-has? helpers. Money is integer minor units. conformance.sh runs
suites on the miniKanren stack and emits scoreboard.{json,md}.

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

lib/commerce/scoreboard.md

@@ -0,0 +1,8 @@
+# commerce Conformance Scoreboard
+
+_Generated by `lib/commerce/conformance.sh`_
+
+| Suite | Pass | Fail | Total |
+|-------|-----:|-----:|------:|
+| catalog | 16 | 0 | 16 |
+| **Total** | **16** | **0** | **16** |