Move account page URLs from blog to federation

Auth templates and widget nav links now point to
federation_url instead of blog_url, co-locating the
account UI with the auth system in the federation app.

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

services/widget_registry.py

@@ -48,8 +48,8 @@ class _WidgetRegistry:
         slug = w.slug
 
         def _href(s=slug):
-            from shared.infrastructure.urls import blog_url
-            return blog_url(f"/auth/{s}/")
+            from shared.infrastructure.urls import federation_url
+            return federation_url(f"/auth/{s}/")
 
         self._account_nav.append(AccountNavLink(
             label=w.label,