maude: Phase 4 conditional equations (19 tests, 138 total)

lib/maude/conditional.sx — condition-aware reducer. ceq fires only when
its guard holds: equational guards (l=r reduce to same normal form) and
boolean guards (term reduces to true), evaluated by recursing through the
same reducer. Verified on gcd, insertion sort, max, even.

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

lib/maude/conformance.conf

@@ -10,10 +10,12 @@ PRELOADS=(
   lib/maude/parser.sx
   lib/maude/reduce.sx
   lib/maude/matching.sx
+  lib/maude/conditional.sx
 )
 
 SUITES=(
   "parse:lib/maude/tests/parse.sx:(mau-parse-tests-run!)"
   "reduce:lib/maude/tests/reduce.sx:(mau-reduce-tests-run!)"
   "matching:lib/maude/tests/matching.sx:(mau-matching-tests-run!)"
+  "conditional:lib/maude/tests/conditional.sx:(mau-conditional-tests-run!)"
 )