Star hackathons into a universal favorites list

Every hackathon card and detail page now carries a star. Tap it and the event drops into one personal favorites list that follows you across the whole site, so the weekend you spotted on the map is still there when you open the database an hour later.

It's a single universal list rather than a folder per view, which keeps the mental model simple: if it matters to you, star it, and it's all in one place. Favorites are tied to your account, so the list is the same whether you're on your laptop or your phone.