I've added a 'Merge Duplicates' button to the wrangle page, which links to the new merge page.
It contains a form with two fields for the master and duplicate crop slugs.
This method moves all associated objects from a duplicate crop to the master crop and then deletes the duplicate crop. The entire operation is wrapped in a database transaction.
I've updated the `merge` action in `crops_controller.rb` to prevent a crop from being merged with itself. The implementation of the controller action is now complete.