artdag: miniKanren CLP(FD) scheduler (schedule.sx) + 15 tests

lib/artdag/schedule.sx on lib/minikanren: slot var per node, fd-lt per edge, fd-label
search. schedule-asap (smallest-first labeling) agrees exactly with plan.sx greedy Kahn
waves (cross-validated); schedules enumerates all valid schedules; schedules-capped
filters to <=cap per slot; schedule-valid? independent dep check. Adds a 'schedule' suite
to conformance.sh loading the minikanren CLP(FD) stack. Completes the optional Phase 3/7
miniKanren box. schedule 15/15, total 213/213.

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

lib/artdag/scoreboard.json

@@ -10,9 +10,10 @@
     "serialize": {"pass": 13, "fail": 0},
     "stats": {"pass": 12, "fail": 0},
     "fault": {"pass": 14, "fail": 0},
-    "maude-optimize": {"pass": 40, "fail": 0}
+    "maude-optimize": {"pass": 40, "fail": 0},
+    "schedule": {"pass": 15, "fail": 0}
   },
-  "total_pass": 198,
+  "total_pass": 213,
   "total_fail": 0,
-  "total": 198
+  "total": 213
 }