This is a cool way to interpret the theme! But sadly I don't think CCGs are very well suited for ludum dare due to the complexity involved in designing and making a good CCG, and this game really shows why. The base CCG mechanics themselves work great, but there is little to no strategy involved in the game, even when playing against another human being. Generally, most cards that allow you to gain more energy should be played immediately, same with building unless they have significant energy costs. The game essentially boils down to luck as whoever gets more of the energy stealing cards would probably win easily. However, these problems can't really be fixed in the short span of 48h or even 72h for the jam, so I think this is about as good as one can get for a game jam.
I think one way to make the game better is to allow players to see what cards the opponents have played and cards that are still in effect, so there is at least a foundation for strategies to be built upon instead of each player just playing their own hand in the best way that they can.
Functionally it is a great game and its pretty fun for a couple of games, but its lacking in a lot of aspects that make CCGs what they are. If you were experimenting with making a CCG game, then I think this is a great result.