Tell scheduling apart from unpublishing in the history

Giving a record a future date was recorded as "unpublished", and announced
to webhooks as such. The history now compares before and after.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lang/en/panel.php

@@ -620,6 +620,7 @@ return [
             'updated' => 'Edited',
             'published' => 'Published',
             'unpublished' => 'Unpublished',
+            'scheduled' => 'Scheduled',
             'deleted' => 'Deleted',
             'restored' => 'Recovered',
             'erased' => 'Erased for good',