Externalize sexp to .sexpr files + render() API

Replace all 676 inline sexp() string calls across 7 services with
render(component_name, **kwargs) calls backed by 46 external .sexpr
component definition files (587 defcomps total).

- Add render() function to shared/sexp/jinja_bridge.py
- Add load_service_components() helper and update load_sexp_dir() for *.sexpr
- Update parser keyword regex to support HTMX hx-on::event syntax
- Convert remaining inline HTML in route files to render() calls
- Add shared/sexp/templates/misc.sexp for cross-service utility components

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

blog/bp/admin/routes.py

@@ -59,7 +59,8 @@ def register(url_prefix):
         await clear_all_cache()
         if is_htmx_request():
             now = datetime.now()
-            html = f'<span class="text-green-600 font-bold">Cache cleared at {now.strftime("%H:%M:%S")}</span>'
+            from shared.sexp.jinja_bridge import render as render_comp
+            html = render_comp("cache-cleared", time_str=now.strftime("%H:%M:%S"))
             return html
 
         return redirect(url_for("settings.cache"))