Revert iterative cek_run, restore working WASM kernel

Iterative cek_run broke page-script parsing in browser. Reverted to
recursive — bytecode compilation overflow handled by native Sx_compiler.

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

hosts/ocaml/lib/sx_ref.ml

@@ -374,16 +374,11 @@ and expand_macro mac raw_args env =
 
 (* cek-run *)
 and cek_run state =
-  (* Iterative loop — no stack growth. Essential for WASM where JS stack is limited. *)
-  let s = ref state in
-  (try
-    while not (match cek_terminal_p !s with Bool true -> true | _ -> false) do
-      s := cek_step !s
-    done;
-    cek_value !s
-  with Eval_error msg ->
-    (if !_last_error_kont = Nil then _last_error_kont := cek_kont !s);
-    raise (Eval_error msg))
+  (if sx_truthy ((cek_terminal_p (state))) then (cek_value (state)) else
+   try cek_run ((cek_step (state)))
+   with Eval_error msg ->
+     (if !_last_error_kont = Nil then _last_error_kont := cek_kont state);
+     raise (Eval_error msg))
 
 (* cek-step *)
 and cek_step state =