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>

account/bp/fragments/routes.py

@@ -1,6 +1,6 @@
 """Account app fragment endpoints.
 
-Exposes HTML fragments at ``/internal/fragments/<type>`` for consumption
+Exposes sexp fragments at ``/internal/fragments/<type>`` for consumption
 by other coop apps via the fragment client.
 
 Fragments:
@@ -18,18 +18,17 @@ def register():
     bp = Blueprint("fragments", __name__, url_prefix="/internal/fragments")
 
     # ---------------------------------------------------------------
-    # Fragment handlers
+    # Fragment handlers — return sexp source text
     # ---------------------------------------------------------------
 
     async def _auth_menu():
         from shared.infrastructure.urls import account_url
-        from shared.sexp.jinja_bridge import sexp as render_sexp
+        from shared.sexp.helpers import sexp_call
 
         user_email = request.args.get("email", "")
-        return render_sexp(
-            '(~auth-menu :user-email user-email :account-url account-url)',
-            **{"user-email": user_email or None, "account-url": account_url("")},
-        )
+        return sexp_call("auth-menu",
+                         user_email=user_email or None,
+                         account_url=account_url(""))
 
     _handlers = {
         "auth-menu": _auth_menu,
@@ -48,8 +47,8 @@ def register():
     async def get_fragment(fragment_type: str):
         handler = _handlers.get(fragment_type)
         if handler is None:
-            return Response("", status=200, content_type="text/html")
-        html = await handler()
-        return Response(html, status=200, content_type="text/html")
+            return Response("", status=200, content_type="text/sexp")
+        src = await handler()
+        return Response(src, status=200, content_type="text/sexp")
 
     return bp