Fix compiler: handle clause-syntax cond — (cond (test body) ...)

compile-cond expected flat syntax (cond test body test body ...) but
hs-parse uses clause syntax (cond (test body) (test body) ...). The
compiler treated the whole clause as the test expression, compiling
((and ...) (do ...)) as a function call — which tried to call the
and-result as a function, producing "not callable: false" JIT errors.

Now detects clause syntax (first arg is a list whose first element is
also a list) and flattens to the expected format before compilation.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/compiler.sx

@@ -724,14 +724,17 @@
       compile-cond
       (fn
         (em args scope tail?)
-        "Compile (cond test1 body1 test2 body2 ... :else fallback)."
+        "Compile (cond test1 body1 test2 body2 ... :else fallback).\n     Also handles clause syntax: (cond (test1 body1) (test2 body2) ...)."
+        (let
+          ((flat-args (if (and (not (empty? args)) (list? (first args)) (> (len (first args)) 1) (list? (first (first args)))) (reduce (fn (acc clause) (if (list? clause) (append acc clause) (append acc (list clause)))) (list) args) args)))
           (if
-          (< (len args) 2)
+            (< (len flat-args) 2)
             (emit-op em 2)
             (let
-            ((test (first args))
+              ((test (nth flat-args 0))
-              (body (nth args 1))
+                (body (nth flat-args 1))
-              (rest-clauses (if (> (len args) 2) (slice args 2) (list))))
+                (rest-clauses
+                  (if (> (len flat-args) 2) (slice flat-args 2) (list))))
               (if
                 (or
                   (and
@@ -755,7 +758,7 @@
                       (patch-i16
                         em
                         end-jump
-                      (- (current-offset em) (+ end-jump 2)))))))))))
+                        (- (current-offset em) (+ end-jump 2))))))))))))
     (define
       compile-case
       (fn