Drop the media translation delete button from the spec; scripting API remains the only delete path.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

specs/engine_side_effects.allium

@@ -280,6 +280,8 @@ rule UpsertMediaTranslationSideEffects {
 
 rule DeleteMediaTranslationSideEffects {
     when: MediaTranslationDeleted(media, language)
+    -- No UI affordance; reached only via the scripting API
+    -- (script.allium bds.media.delete_translation)
     ensures: TranslatedSidecarDeleted(media, language)
 }