Consider deferring sys.path mutation in script_utils to avoid side effects

[coderabbitai]

Context

This issue was created as a follow-up from PR #163.

Problem

The module-level call to _ensure_repo_root_on_sys_path() mutates sys.path on import, which can have unintended side effects.

Recommendation

Consider deferring this to an explicit setup step or scoping it more narrowly to avoid polluting imports in unrelated contexts.

References

• PR: Ensure linux packages script_utils can load cmd utils under uv #163
• Requested by: @leynos