As for just a UI over Zoekt, let me plug https://github.com/TreeTide/underhood/tree/develop#getting-s.... Uses https://github.com/TreeTide/zoekt-underhood.
Zoekt already has its own UI, though it is very feature-limited and lacks syntax highlighting. Demo: https://cs.bazel.build/
If you’re curious about the source, as I was, here it is: https://github.com/sourcegraph/zoekt/blob/main/web/templates...
There's also Neogrok, which is quite nice!
https://github.com/isker/neogrok
https://neogrok-demo-web.fly.dev/