commerce: order lifecycle as a durable flow-on-sx flow (21 tests) — Phase 3 done

order.sx — reserve -> await-payment -> fulfil as a flow-on-sx flow carrying
only the order-id; the SX driver services each request by appending to the
persist ledger. order-begin! creates+reserves and suspends at payment;
order-settle! (webhook) resumes -> fulfils, idempotent on replay
(:already-settled). order-flow-restart! simulates a process restart Scheme-side
and the suspended order resumes with the ledger intact. Composes all three
substrates: minikanren pricing -> flow lifecycle -> persist ledger.
Total 153/153 across 9 suites.

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

lib/commerce/scoreboard.json

@@ -7,9 +7,10 @@
     "promo": {"pass": 17, "fail": 0},
     "stack": {"pass": 16, "fail": 0},
     "quote": {"pass": 13, "fail": 0},
-    "ledger": {"pass": 20, "fail": 0}
+    "ledger": {"pass": 20, "fail": 0},
+    "order": {"pass": 21, "fail": 0}
   },
-  "total_pass": 132,
+  "total_pass": 153,
   "total_fail": 0,
-  "total": 132
+  "total": 153
 }