Sorry about the download button. Two things were going on: the pricing config was wrong (fixed, it's free), and itch locks file uploads while jam voting is running, so I can't attach the downloadable file until voting ends. It goes up the minute the lock lifts. Until then the whole game is the page source, one HTML file, view-source and save it and it runs offline.
On the leaderboard: the global board is the only online piece, and the game is built to lose it gracefully. When that server eventually dies, the game keeps playing, forever.
"Challenge a Friend" is the peer-leaderboard you are talking about for eol. The code carries the lake seed and my pace, your friend races my ghost on the same water, and no server is involved at all. Those codes will still work when the leaderboard is long gone.
Thanks for playing it and for the real feedback.