Fix logout: post to local /auth/logout/ not federation

Each app has its own session and OAuth logout endpoint now.

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

browser/templates/_types/auth/_main_panel.html

@@ -18,7 +18,7 @@
           {% endif %}
         {% endif %}
       </div>
-      <form action="{{ federation_url('/auth/logout/') }}" method="post">
+      <form action="/auth/logout/" method="post">
         <input type="hidden" name="csrf_token" value="{{ csrf_token() }}">
         <button
           type="submit"