Provide versioned, checksummed release binaries

`install-standalone.sh` has the following issues from the perspectives of dependency pinning and supply chain security.

From [`install-standalone.sh`](https://github.com/autifyhq/autify-cli/blob/main/autify-cli/install-standalone.sh):

```bash
URL=https://$AUTIFY_S3_BUCKET.s3.amazonaws.com/$AUTIFY_S3_PREFIX-$OS-$ARCH.$TAR_EXT
curl "$URL" | tar "$TAR_ARGS"
```

1. **The URL does not include a version**, so the same CI configuration can install a different binary depending on when it runs. It cannot be pinned via a lockfile.
2. **There is no checksum or signature verification.** The script pipes `curl` directly into `tar`, so tampering with the distribution source cannot be detected.
3. **The `curl | sudo bash` pattern** leaves no path for users to inspect the content locally before executing it. If the distributed bash uploader were tampered with — as in the [Codecov incident (2021)](https://about.codecov.io/security-update/), where CI environment variables were leaked — users would have no way to defend themselves.

## Proposal

Per-platform binaries are already produced as `$OS-$ARCH.tar.xz`, so it would be a significant improvement to additionally publish:

- **Stable URLs that include the version** (e.g. `…/v0.73.1/autify-darwin-arm64.tar.xz`)
- **SHA256 checksum files**
- Ideally, binaries attached to GitHub Releases

This would enable version pinning via mise/asdf, user-side tamper verification, and installation in rootless environments (Dev Containers, CI containers, etc.).