Change tootctl to use inline parallelization instead of Sidekiq (#11776)

- Remove --background option
- Add --concurrency(=5) option
- Add progress bars

app/models/preview_card.rb

@@ -43,6 +43,8 @@ class PreviewCard < ApplicationRecord
   validates_attachment_size :image, less_than: LIMIT
   remotable_attachment :image, LIMIT
 
+  scope :cached, -> { where.not(image_file_name: [nil, '']) }
+
   before_save :extract_dimensions, if: :link?
 
   def save_with_optional_image!