Handler source: highlight as SX not Python

Handler source is now SX (from defhandler forms), not Python.
Default handler-lang changed from "python" to "sx".

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

sx/sx/examples.sx

@@ -40,7 +40,7 @@
       (~examples/source
         :src-code (highlight
           (join "\n\n" (map handler-source handler-names))
-          (if handler-lang handler-lang "python"))))
+          (if handler-lang handler-lang "sx"))))
     (div
       :class "flex items-center justify-between mt-6"
       (h3 :class "text-lg font-semibold text-stone-700" "Wire response")