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/scoreboard.json

@@ -5,9 +5,10 @@
     "price": {"pass": 20, "fail": 0},
     "api": {"pass": 12, "fail": 0},
     "promo": {"pass": 17, "fail": 0},
-    "stack": {"pass": 16, "fail": 0}
+    "stack": {"pass": 16, "fail": 0},
+    "quote": {"pass": 13, "fail": 0}
   },
-  "total_pass": 99,
+  "total_pass": 112,
   "total_fail": 0,
-  "total": 99
+  "total": 112
 }