Check root Python script formatting in CI

[anp-oai]

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.

[anp-oai]

Waiting for #24983 before landing.