feat: add fediverse follow me sidebar widget

Reuses the existing fediverseInteract Alpine.js component to let
visitors follow the site author from their own fediverse instance.
Registered in all three sidebar routers (homepage, blog listing,
blog post) as widget type "fediverse-follow".

_includes/components/blog-sidebar.njk

@@ -42,6 +42,8 @@
         <script>initPagefind("#blog-sidebar-search");</script>
       </div>
       </is-land>
+    {% elif widget.type == "fediverse-follow" %}
+      {% include "components/widgets/fediverse-follow.njk" %}
     {% elif widget.type == "custom-html" %}
       {% set wConfig = widget.config or {} %}
       <is-land on:visible>