Fix empty code blocks: rename ~docs/code param, fix batched IO dispatch

Two bugs caused code blocks to render empty across the site:

1. ~docs/code component had parameter named `code` which collided with
   the HTML <code> tag name. Renamed to `src` and updated all 57
   callers. Added font-mono class for explicit monospace.

2. Batched IO dispatch in ocaml_bridge.py only skipped one leading
   number (batch ID) but the format has two (epoch + ID):
   (io-request EPOCH ID "name" args...). Changed to skip all leading
   numbers so the string name is correctly found. This fixes highlight
   and other batchable helpers returning empty results.

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

sx/sx/docs.sx

@@ -159,4 +159,4 @@
       (p :class "text-xs text-stone-500"
         (span :class "font-semibold" "Tail position: ") tail-position))
     (when (not (= example ""))
-      (~docs/code :code (highlight example "lisp")))))
+      (~docs/code :src (highlight example "lisp")))))