commerce: order ledger on persist + idempotent reconciliation (20 tests)

ledger.sx — each order is an append-only persist stream "order/<id>";
status/total/paid/recon are folds over events (ledger = source of truth).
order-pay / order-refund are idempotent via persist/append-once keyed on the
payment ref, so a replayed SumUp webhook records once. order-recon-of
classifies unpaid/ok/underpaid/overpaid on net vs total; ledger-mismatches
finds genuine paid != ordered across streams. minikanren+scheme/flow+persist
verified coexisting in one process. Total 132/132 across 8 suites.

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

lib/commerce/scoreboard.md

@@ -11,4 +11,5 @@ _Generated by `lib/commerce/conformance.sh`_
 | promo | 17 | 0 | 17 |
 | stack | 16 | 0 | 16 |
 | quote | 13 | 0 | 13 |
-| **Total** | **112** | **0** | **112** |
+| ledger | 20 | 0 | 20 |
+| **Total** | **132** | **0** | **132** |