Fix root top-bar account link to point to federation

The logged-in user links in _full_user.html (desktop + mobile)
still used blog_url — now they use federation_url to match
the account page migration.

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

browser/templates/_types/root/_full_user.html

@@ -1,5 +1,5 @@
  
-{% set href=blog_url('/auth/account/') %}
+{% set href=federation_url('/auth/account/') %}
 <a
     href="{{ href }}"
     class="justify-center cursor-pointer flex flex-row items-center p-3 gap-2 rounded bg-stone-200 text-black {{select_colours}}"

browser/templates/_types/root/mobile/_full_user.html

@@ -1,5 +1,5 @@
  
-{% set href=blog_url('/auth/account/') %}
+{% set href=federation_url('/auth/account/') %}
 <a
     href="{{ href }}"
     data-close-details