Add published_at attribute to preview cards (#26153)

app/lib/link_details_extractor.rb

@@ -124,7 +124,7 @@ class LinkDetailsExtractor
       author_url: author_url || '',
       embed_url: embed_url || '',
       language: language,
-      created_at: published_at.presence || Time.now.utc,
+      published_at: published_at.presence,
     }
   end
 

app/models/preview_card.rb

@@ -30,6 +30,7 @@
 #  max_score_at                 :datetime
 #  trendable                    :boolean
 #  link_type                    :integer
+#  published_at                 :datetime
 #
 
 class PreviewCard < ApplicationRecord

app/serializers/rest/preview_card_serializer.rb

@@ -15,8 +15,4 @@ class REST::PreviewCardSerializer < ActiveModel::Serializer
   def html
     Sanitize.fragment(object.html, Sanitize::Config::MASTODON_OEMBED)
   end
-
-  def published_at
-    object.created_at
-  end
 end