fix(comments): stop Escape propagation in edit mode

Pressing Escape while editing a comment now only cancels the edit,
without propagating to the parent (which closes the transcribe panel).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/CommentThread.svelte

@@ -169,6 +169,7 @@ function handleEditKeydown(e: KeyboardEvent, commentId: string) {
 		e.preventDefault();
 		saveEdit(commentId);
 	} else if (e.key === 'Escape') {
+		e.stopPropagation();
 		cancelEdit();
 	}
 }