Release: Discovery ships only linux-amd64 binaries and no discoveryctl

## Use Case

A developer on macOS (Apple Silicon) or an ARM Linux host follows a tutorial that needs Discovery next to BREG, Casework and Evidence.

## What we hit

The 0.32.0 release publishes BREG and Casework binaries for `linux-amd64`, `linux-arm64` and `macos-arm64`, but Discovery only for `linux-amd64`. There is no `discoveryctl` asset. On macOS a local composition that includes Discovery has to build it from source or run the container image under emulation.

## Question

Is `linux-amd64` only a deliberate scope for Discovery (image-first deployment, no local CLI story), or a release matrix gap?

- If deliberate: say so in the Discovery install docs and in the release notes asset list, and point local developers to the image.
- If a gap: add `linux-arm64` and `macos-arm64` Discovery binaries, and `discoveryctl` if it is meant to be installed.

Start by comparing the 0.32.0 release asset list with the Discovery install documentation and release notes. Determine whether the missing linux-arm64, macos-arm64, and discoveryctl assets are a release-matrix gap or deliberate scope; done means either the intended limitation is documented or the required assets are published.

Written by the indexing model from the issue text.