Check root Python script formatting in CI (#25165)

## Why

Python files under `scripts/` were not covered by the repository
formatting recipe or the CI formatting job, so formatting drift could
merge unnoticed.

## What

- Add a dedicated `scripts/pyproject.toml` and `scripts/uv.lock` so
root-script formatting uses a locked Ruff version.
- Extend `just fmt` to format root Python scripts and add
`fmt-scripts-check` for CI.
- Run `just fmt-scripts-check` from `.github/workflows/ci.yml`,
installing `uv` through SHA-pinned `astral-sh/setup-uv` while retaining
the `uv` `0.11.3` pin.
- Apply Ruff formatting to the root Python scripts, including
`scripts/just-shell.py`, and extend
`sdk/python/tests/test_artifact_workflow_and_binaries.py` to cover the
root formatting recipe.
- Update `AGENTS.md` so agents run `just fmt` after code changes
anywhere in the repository.

## Validation

- Extended the existing Python SDK workflow test to assert that `just
fmt` includes root Python scripts.

scripts/codex_package/layout.py

@@ -17,7 +17,9 @@ LAYOUT_VERSION = 1
 def prepare_package_dir(package_dir: Path, *, force: bool) -> None:
     if package_dir.exists():
         if not package_dir.is_dir():
-            raise RuntimeError(f"Package output exists and is not a directory: {package_dir}")
+            raise RuntimeError(
+                f"Package output exists and is not a directory: {package_dir}"
+            )
         if any(package_dir.iterdir()):
             if not force:
                 raise RuntimeError(