Delete orders + federation sx_components.py — rendering inlined to routes

Phase 2 (Orders):
- Checkout error/return renders moved directly into route handlers
- Removed orphaned test_sx_helpers.py

Phase 3 (Federation):
- Auth pages use _render_social_auth_page() helper in routes
- Choose-username render inlined into identity routes
- Timeline/search/follow/interaction renders inlined into social routes
  using serializers imported from sxc.pages
- Added _social_page() to sxc/pages/__init__.py for shared use
- Home page renders inline in app.py

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

orders/bp/order/routes.py

@@ -70,9 +70,22 @@ def register() -> Blueprint:
 
         if not hosted_url:
             from shared.sx.page import get_template_context
-            from sx.sx_components import render_checkout_error_page
+            from shared.sx.helpers import render_to_sx, root_header_sx, header_child_sx, full_page_sx, call_url
+            from shared.sx.parser import SxExpr
+            from shared.infrastructure.urls import cart_url
             tctx = await get_template_context()
-            html = await render_checkout_error_page(tctx, error="No hosted checkout URL returned from SumUp when trying to reopen payment.", order=order)
+            account_url = call_url(tctx, "account_url", "")
+            auth_hdr = await render_to_sx("auth-header-row", account_url=account_url)
+            hdr = "(<> " + await root_header_sx(tctx) + " " + await header_child_sx(auth_hdr) + ")"
+            filt = await render_to_sx("checkout-error-header")
+            order_sx = await render_to_sx("checkout-error-order-id", oid=f"#{order.id}")
+            content = await render_to_sx(
+                "checkout-error-content",
+                msg="No hosted checkout URL returned from SumUp when trying to reopen payment.",
+                order=SxExpr(order_sx),
+                back_url=cart_url("/"),
+            )
+            html = await full_page_sx(tctx, header_rows=hdr, filter=filt, content=content)
             return await make_response(html, 500)
 
         return redirect(hosted_url)