commerce: deterministic subtotal + jurisdiction-relational tax (20 tests)

price.sx — cart-subtotal (unit price = base + variant delta, default 0),
taxo facts indexed by (jurisdiction, product-class, customer-class) -> bps
queried both directions, apply-bps half-up integer rounding, cart-total
returning {:subtotal :discounts :tax :total} reproducible from
(context, cart). Total 54/54.

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

lib/commerce/scoreboard.json

@@ -1,9 +1,10 @@
 {
   "suites": {
     "catalog": {"pass": 16, "fail": 0},
-    "cart": {"pass": 18, "fail": 0}
+    "cart": {"pass": 18, "fail": 0},
+    "price": {"pass": 20, "fail": 0}
   },
-  "total_pass": 34,
+  "total_pass": 54,
   "total_fail": 0,
-  "total": 34
+  "total": 54
 }