Wire sexp.js into page template with auto-init and HTMX integration

- Load sexp.js in ~app-layout before body.js
- Auto-process <script type="text/sexp"> tags on DOMContentLoaded
- Re-process after htmx:afterSwap for dynamic content
- Sexp.mount(target, expr, env) for rendering into DOM elements
- Sexp.processScripts() picks up data-components and data-mount tags
- client_components_tag() Python helper serializes Component objects
  back to sexp source for client-side consumption
- 37 parity tests all passing

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sexp/templates/layout.sexp

@@ -70,6 +70,7 @@
                     (when content-html (raw! content-html))
                     (div :class "pb-8"))))))
           (when body-end-html (raw! body-end-html))
+          (script :src (str asset-url "/scripts/sexp.js"))
           (script :src (str asset-url "/scripts/body.js")))))))
 
 (defcomp ~oob-response (&key oobs-html filter-html aside-html menu-html content-html)