This is quite an entry: the deck-builder X auto-battler twist is fun and worth exploring further and the music/sounds are great (and given enough time and effort, would likely be less repetitive—it is the result of a game jam after all).
I do think the UI would need a bit of something to help the player understand where the resources are. I had no idea where on the screen I could find my resource pool until eventually I saw those little yellow circles crammed near the bottom of the screen. Maybe make them wiggle or crack or glow when you grab a card to show how much it would cost? Something to make them stand out as an important piece of information for the player. Also, it's not clear how cards deal damage to the player. I had to study the game and what was happening to figure out that cards were supposed to reach the second-to-last rank in order to deal damage (minus ranged cards). Maybe a bit more of a visual distinction from regular card spaces vs. important player backline spaces?
Building your deck upfront is an interesting choice. I personally find it a weird one, given when you first start a deck-builder you have no idea what the cards/decks will function like, so expecting the player to build their own deck seems almost like setting them up for a failure they will have little ability to learn from. I think maybe just give them a static starting deck, and then let them adjust as they learn the deck and the game progresses.
Honestly, you could flesh this game and its mechanics out into a fun full-fledged deck-builder. Nice job.