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/test_cargo.py

@@ -27,7 +27,9 @@ class SourceBinariesForTargetTest(unittest.TestCase):
             [],
         )
 
-    def test_linux_package_with_prebuilt_entrypoint_and_bwrap_builds_nothing(self) -> None:
+    def test_linux_package_with_prebuilt_entrypoint_and_bwrap_builds_nothing(
+        self,
+    ) -> None:
         self.assertEqual(
             source_binaries_for_target(
                 TARGET_SPECS["x86_64-unknown-linux-musl"],
@@ -40,7 +42,9 @@ class SourceBinariesForTargetTest(unittest.TestCase):
             [],
         )
 
-    def test_windows_package_with_prebuilt_entrypoint_and_helpers_builds_nothing(self) -> None:
+    def test_windows_package_with_prebuilt_entrypoint_and_helpers_builds_nothing(
+        self,
+    ) -> None:
         self.assertEqual(
             source_binaries_for_target(
                 TARGET_SPECS["x86_64-pc-windows-msvc"],