mod: Ext 18 — ergonomic defrule / ruleset surface, 375/375

mod/defrule collects trailing conditions via &rest; mod/ruleset assembles rules.
No macro needed — conditions are plain data, fn supports &rest here. Produces
structurally identical rules to mk-rule (asserted) and works in the engine
unchanged. Closes the roadmap's original defrule surface. +11 tests.

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

lib/mod/conformance.conf

@@ -12,6 +12,7 @@ PRELOADS=(
   lib/prolog/compiler.sx
   lib/mod/schema.sx
   lib/mod/policy.sx
+  lib/mod/defrule.sx
   lib/mod/engine.sx
   lib/mod/explain.sx
   lib/mod/severity.sx
@@ -53,4 +54,5 @@ SUITES=(
   "disjunction:lib/mod/tests/disjunction.sx:(mod-disjunction-tests-run!)"
   "activity:lib/mod/tests/activity.sx:(mod-activity-tests-run!)"
   "policies:lib/mod/tests/policies.sx:(mod-policies-tests-run!)"
+  "defrule:lib/mod/tests/defrule.sx:(mod-defrule-tests-run!)"
 )