datalog: comparison ops require same-type operands

Type-mixed comparisons were silently inconsistent:

  <("hello", 5)  =>  no result, no error  (silent false)
  <(a, 5)        =>  raises "Expected number, got symbol"

Both should fail loudly with a comprehensible message. Added
dl-compare-typeok?: <, <=, >, >= now require both operands to share
a primitive type (both numbers or both strings) and raise a clear
"comparison <op> requires same-type operands" error otherwise.

`!=` is exempted because it's the polymorphic inequality test
built on dl-tuple-equal? — cross-type pairs are legitimately unequal
and the existing semantics for that case match user intuition.

2 new regression tests; conformance 267/267.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/datalog/scoreboard.json

@@ -1,14 +1,14 @@
 {
   "lang": "datalog",
-  "total_passed": 265,
+  "total_passed": 267,
   "total_failed": 0,
-  "total": 265,
+  "total": 267,
   "suites": [
     {"name":"tokenize","passed":30,"failed":0,"total":30},
     {"name":"parse","passed":22,"failed":0,"total":22},
     {"name":"unify","passed":29,"failed":0,"total":29},
     {"name":"eval","passed":40,"failed":0,"total":40},
-    {"name":"builtins","passed":24,"failed":0,"total":24},
+    {"name":"builtins","passed":26,"failed":0,"total":26},
     {"name":"semi_naive","passed":8,"failed":0,"total":8},
     {"name":"negation","passed":10,"failed":0,"total":10},
     {"name":"aggregates","passed":23,"failed":0,"total":23},
@@ -16,5 +16,5 @@
     {"name":"magic","passed":36,"failed":0,"total":36},
     {"name":"demo","passed":21,"failed":0,"total":21}
   ],
-  "generated": "2026-05-11T08:03:45+00:00"
+  "generated": "2026-05-11T08:07:23+00:00"
 }