commerce: time-windowed promotions (19 tests) — Phase 5 ext

window.sx — a validity window kept separate from the promo tuple (promo.sx
untouched): windowed promo (promo from until), inclusive int timestamps, nil =
open bound. active-ruleset filters to promos live at `at` and feeds the existing
promo/stack/quote pipeline; active-codes is the backward "which codes live at
T?" query; windowed-quote is the datetime-aware, deterministic quote.
Total 228/228 across 14 suites.

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

lib/commerce/scoreboard.md

@@ -17,4 +17,5 @@ _Generated by `lib/commerce/conformance.sh`_
 | federation | 12 | 0 | 12 |
 | attribution | 16 | 0 | 16 |
 | payment | 7 | 0 | 7 |
-| **Total** | **209** | **0** | **209** |
+| window | 19 | 0 | 19 |
+| **Total** | **228** | **0** | **228** |