Add select_all.

frontends/ycdl_flask/templates/channel.html

@@ -386,6 +386,15 @@ function toggle_embed_video(video_id)
     }
 }
 
+function select_all()
+{
+    video_card_first_selected = null;
+    for (const video_card of document.getElementsByClassName("video_card"))
+    {
+        video_card.classList.add("video_card_selected");
+    }
+}
+
 function deselect_all()
 {
     video_card_first_selected = null;