maude: Phase 1 parser — fmod/mod modules, signatures, mixfix terms (65 tests)

Term representation (lib/maude/term.sx) plus a module parser
(lib/maude/parser.sx) consuming lib/guest/lex + pratt:

- whitespace+bracket tokenizer (--- / *** comments)
- mixfix classification (split op names on _): infix/prefix/postfix/const
- precedence-climbing term parser over a pratt table built from op decls
- fmod/mod ... endfm/endm with sort/subsort/op/var/eq/ceq/rl/crl
- transitive subsort hierarchy + operator overloading queries

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

lib/maude/conformance.sh

@@ -0,0 +1,3 @@
+#!/usr/bin/env bash
+# Thin wrapper — see lib/guest/conformance.sh and lib/maude/conformance.conf.
+exec bash "$(dirname "$0")/../guest/conformance.sh" "$(dirname "$0")/conformance.conf" "$@"