feat(harness-grok-build): update underlying SDK and add support for `reasoningEffort` control (#19867)

## Background

The Grok Build harness was pinned to an older SDK and could not
configure reasoning effort.

## Summary

This updates the Grok Build runtime and applies model configuration
through `GROK_CONFIG`. The adapter pins a default model while only
specifying reasoning effort when callers configure it.

- Update Grok Build and its ACP bridge dependencies.
- Add the `reasoningEffort` adapter setting and preserve caller model
overrides.
- Add coverage, documentation, and an end-to-end reasoning example.

## End-to-End Verification

Ran:

```sh
./tools/run-harness-agent-examples.sh --harness grok-build --auth direct --example with-reasoning
```

## Checklist

- [x] All commits are signed (PRs with unsigned commits cannot be
merged)
- [x] Tests have been added / updated (for bug fixes / features)
- [x] Documentation has been added / updated (for bug fixes / features)
- [x] A _patch_ changeset for relevant packages has been added (for bug
fixes / features - run `pnpm changeset` in the project root)
- [x] I have reviewed this pull request (self-review)