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>

shared/browser/templates/macros/cart_icon.html

@@ -1,7 +1,7 @@
 {# Cart icon/badge — shows logo when empty, cart icon with count when items present #}
 
 {% macro cart_icon(count=0, oob=False) %}
-<div id="cart-mini" {% if oob %}hx-swap-oob="{{oob}}"{% endif %}>
+<div id="cart-mini" {% if oob %}sx-swap-oob="{{oob}}"{% endif %}>
   {% if count == 0 %}
   <div class="h-12 w-12 rounded-full overflow-hidden border border-stone-300 flex-shrink-0">
     <a