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.

.github/workflows/ci.yml

@@ -74,5 +74,15 @@ jobs:
       - name: Check root README ToC
         run: python3 scripts/readme_toc.py README.md
 
+      - uses: taiki-e/install-action@44c6d64aa62cd779e873306675c7a58e86d6d532 # v2.62.49
+        with:
+          tool: just
+      - name: Install uv
+        uses: astral-sh/setup-uv@08807647e7069bb48b6ef5acd8ec9567f424441b # v8.1.0
+        with:
+          version: "0.11.3"
+      - name: Ruff format Python scripts (run `just fmt` to fix)
+        run: just fmt-scripts-check
+
       - name: Prettier (run `pnpm run format:fix` to fix)
         run: pnpm run format