Provide option to force use of system scrollbar styling (#32117)

app/models/concerns/user/has_settings.rb

@@ -43,6 +43,10 @@ module User::HasSettings
     settings['web.use_system_font']
   end
 
+  def setting_system_scrollbars_ui
+    settings['web.use_system_scrollbars']
+  end
+
   def setting_noindex
     settings['noindex']
   end

app/models/user_settings.rb

@@ -24,6 +24,7 @@ class UserSettings
     setting :use_blurhash, default: true
     setting :use_pending_items, default: false
     setting :use_system_font, default: false
+    setting :use_system_scrollbars, default: false
     setting :disable_swiping, default: false
     setting :disable_hover_cards, default: false
     setting :delete_modal, default: true