* Add specs for ActivityPub::CollectionsController#show

* Raise ActiveRecord::RecordNotFound

Raising ActiveRecord::NotFound raises NameError: uninitialized constant
ActiveRecord::NotFound.

* Federate pinned statuses over ActivityPub

* Display pinned toots in web UI

Fix #6117

* Fix migration

* Fix tests

* Update outbox_serializer.rb

* Update remove_serializer.rb

* Update add_serializer.rb

* Update fetch_featured_collection_service.rb