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>

federation/app.py

@@ -49,14 +49,14 @@ async def federation_context() -> dict:
     if ident["session_id"] is not None:
         cart_params["session_id"] = ident["session_id"]
 
-    cart_mini_html, auth_menu_html, nav_tree_html = await fetch_fragments([
+    cart_mini, auth_menu, nav_tree = await fetch_fragments([
         ("cart", "cart-mini", cart_params or None),
         ("account", "auth-menu", {"email": user.email} if user else None),
         ("blog", "nav-tree", {"app_name": "federation", "path": request.path}),
     ])
-    ctx["cart_mini_html"] = cart_mini_html
-    ctx["auth_menu_html"] = auth_menu_html
-    ctx["nav_tree_html"] = nav_tree_html
+    ctx["cart_mini"] = cart_mini
+    ctx["auth_menu"] = auth_menu
+    ctx["nav_tree"] = nav_tree
 
     # Actor profile for logged-in users
     if g.get("user"):