Fix payments admin link to cart.rose-ash.com/{slug}/admin/payments/

Payments are managed by the cart service, not events.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

blog/sexp/sexp_components.py

@@ -150,7 +150,7 @@ def _post_admin_nav_html(ctx: dict) -> str:
         for url_fn, path, label in [
             (events_url_fn, f"/{slug}/admin/", "calendars"),
             (market_url_fn, f"/{slug}/admin/", "markets"),
-            (events_url_fn, f"/{slug}/payments/", "payments"),
+            (ctx.get("cart_url"), f"/{slug}/admin/payments/", "payments"),
         ]:
             if not callable(url_fn):
                 continue