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>

federation/bp/auth/routes.py

@@ -46,7 +46,7 @@ async def _render_social_auth_page(component: str, title: str, **kwargs) -> str:
     """Render an auth page with social layout — replaces sx_components helpers."""
     from shared.sx.helpers import render_to_sx
     from shared.sx.page import get_template_context
-    from sxc.pages import _social_page
+    from sxc.pages.utils import _social_page
     ctx = await get_template_context()
     content = await render_to_sx(component, **{k: v for k, v in kwargs.items() if v})
     return await _social_page(ctx, None, content=content, title=title)