### Summary
The Go CLI parses `search foo files -n 20` into
`SearchCommandOptions.TopK`, but only forwards the value as `top_k`.
File search reads the independent `SearchOptions.Limit` field, so it
receives zero and falls back to the default page size.
This change forwards the parsed number as both `limit` and `top_k`. File
search can consume `Limit`, while semantic dataset search continues to
consume `TopK`.
A focused regression test covers the full CLI command-to-provider
parameter path.
Fixes#19284
