Fix Jinja2 error: set() is not a builtin, use [] instead

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

templates/federation/_actor_list_items.html

@@ -27,7 +27,7 @@
 
     {% if actor %}
       <div class="flex-shrink-0">
-        {% if list_type == "following" or a.actor_url in (followed_urls or set()) %}
+        {% if list_type == "following" or a.actor_url in (followed_urls or []) %}
           <form method="post" action="{{ url_for('social.unfollow') }}"
                 hx-post="{{ url_for('social.unfollow') }}"
                 hx-target="closest article"

templates/federation/following.html

@@ -7,7 +7,7 @@
 
 <div id="actor-list">
   {% set list_type = "following" %}
-  {% set followed_urls = set() %}
+  {% set followed_urls = [] %}
   {% include "federation/_actor_list_items.html" %}
 </div>
 {% endblock %}