~docs/oob-code: highlight source text

Now calls (highlight text) to produce syntax-colored SX output.
OCaml-side aser has full env so code/span tags resolve correctly.

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

sx/sx/docs.sx

@@ -17,7 +17,7 @@
     :sx-swap-oob "innerHTML"
     (div
       :class "not-prose bg-stone-100 rounded p-4 mt-3"
-      (pre :class "text-sm whitespace-pre-wrap break-words" (code text)))))
+      (pre :class "text-sm whitespace-pre-wrap break-words" (highlight text)))))
 
 (defcomp
   ~docs/attr-table