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>

test/app.py

@@ -21,11 +21,11 @@ async def test_context() -> dict:
         blog_url_str = blog_url("")
     else:
         blog_url_str = str(blog_url or "")
-    ctx["cart_mini_html"] = render(
+    ctx["cart_mini"] = render(
         "cart-mini", cart_count=0, blog_url=blog_url_str, cart_url="",
     )
-    ctx["auth_menu_html"] = ""
-    ctx["nav_tree_html"] = ""
+    ctx["auth_menu"] = ""
+    ctx["nav_tree"] = ""
     return ctx