Merge branch 'main' into glitch-soc/merge-upstream

Conflicts:
- `app/models/account.rb`:
  Not a real conflict, just upstream getting rid of unused constants too close
  to glitch-soc-specific contents.
  Removed unused constants like upstream did.
- `app/models/trends.rb`:
  Conflict because glitch-soc disabled email notifications for trending links.
  Upstream has refactored this quite a bit and added trending posts.
  Took upstream code, but disabling the extra trending stuff will come in
  another commit.
- `app/views/admin/trends/links/index.html.haml`:
  Conflict due to glitch-soc's theming system.
  Ported upstream changes accordingly.

app/views/admin/follow_recommendations/show.html.haml

@@ -6,12 +6,14 @@
 %hr.spacer/
 
 = form_tag admin_follow_recommendations_path, method: 'GET', class: 'simple_form' do
+  - RelationshipFilter::KEYS.each do |key|
+    = hidden_field_tag key, params[key] if params[key].present?
+
   .filters
     .filter-subset.filter-subset--with-select
       %strong= t('admin.follow_recommendations.language')
       .input.select.optional
-        = select_tag :language, options_for_select(I18n.available_locales.map { |key| key.to_s.split(/[_-]/).first.to_sym }.uniq.map { |key| [standard_locale_name(key), key]}, @language)
-
+        = select_tag :language, options_for_select(Trends.available_locales.map { |key| [standard_locale_name(key), key] }, @language)
     .filter-subset
       %strong= t('admin.follow_recommendations.status')
       %ul