Slim sxc/pages/__init__.py for federation, test, cart, blog

Move render functions, layouts, helpers, and utils from __init__.py
to sub-modules (renders.py, layouts.py, helpers.py, utils.py).
Update all bp route imports to point at sub-modules directly.
Each __init__.py is now ≤20 lines of setup + registration.

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 sxc.pages import (
+        from sxc.pages.renders import (
             render_orders_page,
             render_orders_rows,
             render_orders_oob,