A card itself cannot be marked animated; only widgets.
With the "Widgets" tool active, you can set this property from the "Widgets -> Animated" menu item.
If you want an "animated card" you can either use a self-refreshing approach with go[card] like in your original script, or add an animated widget to the card that acts as an "event pump" by allowing the view[] event to bubble up to the card. The Decker Sokoban example uses something similar to the latter approach.