Key management is a critical part of the story, as j2kun has pointed out before. In this demo, we're intentionally caching the same key material for every visitor so we can showcase the actual FHE computation without making everyone wait through client-side key generation and upload. Even as a one-time cost, having each user generate their own keys in the browser and transfer them to the server introduces noticeable setup time, which we felt would get in the way of the experience for a demo. We actually implemented it that way at first; setup wasn't a matter of minutes, but we changed course after worrying about the experience for visitors on mobile data.
This demo is focused on demonstrating the computation itself, not a production-grade key management flow. Supporting per-user keys and a more realistic trust model is definitely on our roadmap for future demos.