chore: Translate en.json in ca [Manual Sync]

99% of minimum 50% translated source file: 'en.json'
on 'ca'.

Sync of partially translated files: 
untranslated content is included with an empty translation 
or source language content depending on file format

frontend/src/i18n/ca.json

@@ -24,7 +24,7 @@
     "ok": "D'acord",
     "permalink": "Enllaç permanent",
     "previous": "Anterior",
-    "preview": "",
+    "preview": "Preview",
     "publish": "Publicar",
     "rename": "Reanomenar",
     "replace": "Substituir",