Send all responses as sexp wire format with client-side rendering

- Server sends sexp source text, client (sexp.js) renders everything
- SexpExpr marker class for nested sexp composition in serialize()
- sexp_page() HTML shell with data-mount="body" for full page loads
- sexp_response() returns text/sexp for OOB/partial responses
- ~app-body layout component replaces ~app-layout (no raw!)
- ~rich-text is the only component using raw! (for CMS HTML content)
- Fragment endpoints return text/sexp, auto-wrapped in SexpExpr
- All _*_html() helpers converted to _*_sexp() returning sexp source
- Head auto-hoist: sexp.js moves meta/title/link/script[ld+json]
  from rendered body to document.head automatically
- Unknown components render warning box instead of crashing page
- Component kwargs preserve AST for lazy rendering (fixes <> in kwargs)
- Fix unterminated paren in events/sexp/tickets.sexpr

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

cart/bp/page_admin/routes.py

@@ -8,6 +8,7 @@ from shared.infrastructure.actions import call_action
 from shared.infrastructure.data_client import fetch_data
 from shared.browser.app.authz import require_admin
 from shared.browser.app.utils.htmx import is_htmx_request
+from shared.sexp.helpers import sexp_response
 
 
 def register():
@@ -23,9 +24,10 @@ def register():
         page_post = getattr(g, "page_post", None)
         if not is_htmx_request():
             html = await render_cart_admin_page(ctx, page_post)
+            return await make_response(html)
         else:
-            html = await render_cart_admin_oob(ctx, page_post)
-        return await make_response(html)
+            sexp_src = await render_cart_admin_oob(ctx, page_post)
+            return sexp_response(sexp_src)
 
     @bp.get("/payments/")
     @require_admin
@@ -37,9 +39,10 @@ def register():
         page_post = getattr(g, "page_post", None)
         if not is_htmx_request():
             html = await render_cart_payments_page(ctx, page_post)
+            return await make_response(html)
         else:
-            html = await render_cart_payments_oob(ctx, page_post)
-        return await make_response(html)
+            sexp_src = await render_cart_payments_oob(ctx, page_post)
+            return sexp_response(sexp_src)
 
     @bp.put("/payments/")
     @require_admin
@@ -78,6 +81,6 @@ def register():
         from sexp.sexp_components import render_cart_payments_panel
         ctx = await get_template_context()
         html = render_cart_payments_panel(ctx)
-        return await make_response(html)
+        return sexp_response(html)
 
     return bp