fix: isTagFollowed false positive for global-only follows; # stripping in getTagsPubActorUrl

- isTagFollowed() now checks doc?.followedAt instead of !!doc, so it
  correctly returns false for global-only follows (document exists but
  no local followedAt)
- getTagsPubActorUrl() strips leading # so URLs like ?tag=%23indieweb
  don't produce invalid https://tags.pub/user/#indieweb actor URLs
- Remove stale "Task 5" plan reference comment in tag timeline template

views/activitypub-tag-timeline.njk

@@ -81,7 +81,7 @@
       </nav>
     {% endif %}
 
-    {# Infinite scroll sentinel (Task 5) #}
+    {# Infinite scroll load-more trigger #}
     {% if before %}
       <div class="ap-load-more"
         id="ap-load-more"