Done to avoid spammy warnings to end up in the model context without
having to switch to nightly
```
Warning: can't set `imports_granularity = Item`, unstable features are only available in nightly channel.
```
## Summary
- move the workspace justfile to the repository root for easier
discovery
- set the just working directory to codex-rs so existing recipes still
run in the Rust workspace
## Testing
- not run (not requested)
------
[Codex
Task](https://chatgpt.com/codex/tasks/task_i_69334db473108329b0cc253b7fd8218e)