Restore recursive cek_run, remove step counter/limit

The iterative cek_run with Atomic step counting and debug prints
added overhead and complexity. The debug print called value_to_str
twice per million steps which could be very slow on large expressions.

Restore the original recursive cek_run from before the iterative
conversion. Remove the step limit mechanism (was causing render
timeouts). The recursive version is simpler and proven.

1166 passed, 0 failed.

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

hosts/ocaml/bin/sx_server.ml

@@ -2017,9 +2017,6 @@ let http_mode port =
       in
       match work with
       | Some (fd, path, headers) ->
-        (* ~10M steps ≈ 3-5 seconds of CEK evaluation *)
-        Atomic.set Sx_ref._step_count 0;
-        Atomic.set Sx_ref._step_limit 10_000_000;
         let response =
           try
             let is_ajax = List.exists (fun (k, _) -> k = "sx-request" || k = "hx-request") headers in
@@ -2035,7 +2032,6 @@ let http_mode port =
             Printf.eprintf "[render] Error for %s: %s\n%!" path (Printexc.to_string e);
             http_response ~status:500 "<h1>Internal Server Error</h1>"
         in
-        Atomic.set Sx_ref._step_limit 0;
         write_response fd response
       | None -> ()
     done