ocaml: phase 5.1 queens.ml baseline (15/15 pass)

4-queens via recursive backtracking + List.fold_left. Returns 2 (the
two solutions of 4-queens). Per-program timeout in run.sh bumped to
240s — the tree-walking interpreter is slow on heavy recursion but
correct.

The substrate handles full backtracking + safe-check recursion +
list-driven candidate enumeration end-to-end.

lib/ocaml/baseline/run.sh

@@ -36,7 +36,7 @@ for f in lib/ocaml/baseline/*.ml; do
 (eval "(ocaml-run-program (file-read \"$f\"))")
 EOF
 
-  output=$(timeout 120 "$SX_SERVER" < "$TMP" 2>/dev/null)
+  output=$(timeout 240 "$SX_SERVER" < "$TMP" 2>/dev/null)
   rm -f "$TMP"
 
   result=$(echo "$output" | awk '