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/plans/self-hosting-bootstrapper.sx

@@ -176,7 +176,7 @@
         (p "Python closures can read but not rebind outer variables. "
            (code "py.sx") " detects " (code "set!") " targets that cross lambda boundaries "
            "and routes them through a " (code "_cells") " dict:")
-        (~docs/code :code (highlight ";; SX                              ;; Python
+        (~docs/code :src (highlight ";; SX                              ;; Python
 (define counter                    def counter():
   (fn ()                               _cells = {}
     (let ((n 0))                       _cells['n'] = 0