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.json

@@ -0,0 +1,8 @@
+{
+  "suites": {
+    "catalog": {"pass": 16, "fail": 0}
+  },
+  "total_pass": 16,
+  "total_fail": 0,
+  "total": 16
+}