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>

events/sexp/header.sexpr

@@ -20,7 +20,7 @@
     (i :class "fa fa-calendar-day")
     (span date-str)))
 
-(defcomp ~events-entry-label (&key entry-id title-html times-html)
+(defcomp ~events-entry-label (&key entry-id title times)
   (div :id (str "entry-title-" entry-id) :class "flex gap-1 items-center"
-    (raw! title-html) (raw! times-html)))
+    title times))