Add CSRF token to logout form in base template

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

templates/federation/base.html

@@ -20,6 +20,7 @@
             <a href="{{ url_for('identity.choose_username_form') }}" class="hover:underline">Choose username</a>
           {% endif %}
           <form method="post" action="{{ url_for('auth.logout') }}" class="inline">
+            <input type="hidden" name="csrf_token" value="{{ csrf_token() }}">
             <button type="submit" class="hover:underline">Logout</button>
           </form>
         {% else %}