commerce: composed priced quote (price+promo+stacking) (13 tests)

quote.sx — cart-quote composes the pipeline into a deterministic
{:subtotal :discount :tax :total :codes} with total = subtotal - discount +
tax. Explicit tax policy: tax on gross per-line amounts (discount reduces
payable, not the tax base). This quote is the value the Phase-3 order flow
carries. Total 112/112 across 7 suites.

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 price api promo stack)
+SUITES=(catalog cart price api promo stack quote)
 
 OUT_JSON="lib/commerce/scoreboard.json"
 OUT_MD="lib/commerce/scoreboard.md"
@@ -49,6 +49,7 @@ run_suite() {
 (load "lib/commerce/api.sx")
 (load "lib/commerce/promo.sx")
 (load "lib/commerce/stack.sx")
+(load "lib/commerce/quote.sx")
 (epoch 2)
 (eval "(define ct-pass 0)")
 (eval "(define ct-fail 0)")