The dynamically calculated `NumCtx` value wasn't making it all the way
to the chat handler
This fix made us notice that the minimum setting of `NumCtx` to 4 inside
of `server/sched.go` was accidentally removed in #10364. The minimum
doesn't make it out to the client code, which is important for
embeddings, as demonstrated in `TestAllMiniLMEmbedTruncate`. This should
be cleaned up more, but probably is caused by start and end tokens in
the embedding, so small context sizes need some work there. See the
comment in `server/routes.go` for more information on the temporary hack
that's been added to propagate the dynamically calculated `NumCtx` (the
-1 guard there is to keep embeddings working if you set `NumCtx` to some
small value like `1`).
Fixes: #10441
d20cd8df80