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/page_admin/routes.py

@@ -47,7 +47,7 @@ def register():
         g.page_config = SimpleNamespace(**raw_pc) if raw_pc else None
 
         from shared.sx.page import get_template_context
-        from sxc.pages import render_cart_payments_panel
+        from sxc.pages.renders import render_cart_payments_panel
         ctx = await get_template_context()
         html = await render_cart_payments_panel(ctx)
         return sx_response(html)