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/conformance.sh

@@ -17,7 +17,7 @@ if [ ! -x "$SX_SERVER" ]; then
   exit 1
 fi
 
-SUITES=(catalog cart)
+SUITES=(catalog cart price)
 
 OUT_JSON="lib/commerce/scoreboard.json"
 OUT_MD="lib/commerce/scoreboard.md"
@@ -45,6 +45,7 @@ run_suite() {
 (load "lib/minikanren/defrel.sx")
 (load "lib/commerce/catalog.sx")
 (load "lib/commerce/cart.sx")
+(load "lib/commerce/price.sx")
 (epoch 2)
 (eval "(define ct-pass 0)")
 (eval "(define ct-fail 0)")