I'm going to start off by saying that it's incredibly impressive that you made this without a game engine. Absolutely well done. I know C is a hard language to work in, and then also getting it to run in browser and having a finished product for the jam is awesome!
I also wanted to mention that I wasn't sure about like how much money I had, of if my deals were good or bad. It'd be cool to have that feedback. Or maybe those things were there and I missed them. Also it'd be cool to have some more card information when you're selecting the card that you want to use.
The art is super cute! I'm so jealous of your skills! Also, I understand what it's like to run out of time for the music. I did the same with my game, and I was working with an existing engine. Great job!