Hey! This is an interesting idea and I think you should definitely continue to refine it after the jam. I also liked the rune art. My main criticisms I figure you might be considering already but I'll throw them out there.
There should be a more apparent way to disconnect runes. I know you can override connections, but the screen gets particularly messy when making multiple connections. Maybe treat the rune catalog as a designated boundary. That way, when you drag a rune back to the catalog, it disconnects and returns to it's original position. That might make it look a little more organized.
The other thing is it's not readily apparent how runes should be combined, so I think some predefined examples/information on what to combine might be a good idea.
Other than that I like what you have so far. It would be interesting to see this combined as a module for some top-down defense game or something.