use sqllite vec for RAG

[jlewi]

Now that we are starting to use sqllite (#253) it might be worth using sqllite vec.

That said we aren't using cgo. I think sqllite-vec would require us to use cgo because it is written in C. So we'd need to figure out how to link in the C based version of sllite-vec.

[jlewi]

There are CGO versions and WASM based versions that don't require CGO.
https://github.com/asg017/sqlite-vec-go-bindings