Phase 4: Delete cart/sx/sx_components.py, move renders to sxc/pages

Move all render functions (orders page/rows/oob, order detail/oob,
checkout error, payments panel), header helpers, and serializers from
cart/sx/sx_components.py into cart/sxc/pages/__init__.py. Update all
route imports from sx.sx_components to sxc.pages. Replace
import sx.sx_components in app.py with load_service_components("cart").

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

cart/bp/orders/routes.py

@@ -138,7 +138,7 @@ def register(url_prefix: str) -> Blueprint:
         orders = result.scalars().all()
 
         from shared.sx.page import get_template_context
-        from sx.sx_components import (
+        from sxc.pages import (
             render_orders_page,
             render_orders_rows,
             render_orders_oob,