maude: order-sorted least-sort inference (14 tests, 250 total)

lib/maude/sorts.sx — mau/term-sort computes the least sort of a term (smallest
result sort among op declarations whose arg sorts the actuals satisfy modulo
subsorting); overloaded f(1)=NzNat vs f(s 0)=Nat. mau/has-sort? for
membership-style checks. Answers the plan's order-sorted substrate question.

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

lib/maude/scoreboard.md

@@ -1,6 +1,6 @@
 # maude scoreboard
 
-**236 / 236 passing** (0 failure(s)).
+**250 / 250 passing** (0 failure(s)).
 
 | Suite | Passed | Total | Status |
 |-------|--------|-------|--------|
@@ -10,6 +10,7 @@
 | conditional | 19 | 19 | ok |
 | owise | 8 | 8 | ok |
 | gather | 7 | 7 | ok |
+| sorts | 14 | 14 | ok |
 | rewrite | 21 | 21 | ok |
 | searchpath | 8 | 8 | ok |
 | strategy | 19 | 19 | ok |