Replace 21 Jinja render_template() calls with sx render functions

Phase 1: Wire 16 events routes to existing sx render functions
- slot, slots, ticket_types, ticket_type, calendar_entries,
  calendar_entry, calendar_entry/admin

Phase 2: Orders checkout return (2 calls)
- New orders/sx/checkout.sx with return page components
- New render_checkout_return_page() in orders/sx/sx_components.py

Phase 3: Blog menu items (3 calls)
- New blog/sx/menu_items.sx with search result components
- New render_menu_item_form() and render_page_search_results()
  in blog/sx/sx_components.py

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

orders/bp/checkout/routes.py

@@ -1,7 +1,7 @@
 """Checkout webhook + return routes (moved from cart/bp/cart/global_routes.py)."""
 from __future__ import annotations
 
-from quart import Blueprint, g, request, render_template, make_response
+from quart import Blueprint, g, request, make_response
 from sqlalchemy import select
 
 from shared.models.order import Order
@@ -46,12 +46,13 @@ def register() -> Blueprint:
     @bp.get("/return/<int:order_id>/")
     async def checkout_return(order_id: int):
         """Handle the browser returning from SumUp after payment."""
+        from shared.sx.page import get_template_context
+        from sx.sx_components import render_checkout_return_page
+
         order = await get_order_with_details(g.s, order_id)
         if not order:
-            html = await render_template(
-                "_types/cart/checkout_return.html",
-                order=None, status="missing", calendar_entries=[],
-            )
+            tctx = await get_template_context()
+            html = await render_checkout_return_page(tctx, order=None, status="missing")
             return await make_response(html)
 
         if order.page_config_id:
@@ -88,9 +89,9 @@ def register() -> Blueprint:
         order_tickets = [dto_from_dict(TicketDTO, t) for t in raw_tickets]
         await g.s.flush()
 
-        html = await render_template(
-            "_types/cart/checkout_return.html",
-            order=order, status=status,
+        tctx = await get_template_context()
+        html = await render_checkout_return_page(
+            tctx, order=order, status=status,
             calendar_entries=calendar_entries,
             order_tickets=order_tickets,
         )