Add basedpyright pre-commit hook to match canonical linting

[ModeSevenIndustrialSolutions]

Summary

The canonical pre-commit linting setup in actions-template includes the basedpyright type-checker hook. This repository ships Python helper code but its .pre-commit-config.yaml is missing that hook. This issue tracks adding it.

Canonical hook block

  # Requires a mirror, primary repo lacks .pre-commit-hooks.yaml
  - repo: https://github.com/DetachHead/basedpyright-prek-mirror
    rev: d55eabd2531b4f4a4c49c30fba627ce3a636ab79  # frozen: 1.39.9
    hooks:
      - id: basedpyright

Insert this block into the existing config; preserve any repo-specific customizations rather than wholesale-copying the canonical file.

Current state (basedpyright 1.39.9)

• [tool.basedpyright] config: absent (no pyproject.toml)
• Baseline scan (default "recommended" mode): 0 errors, 0 warnings ✅

Remediation needed

Minimal — this is a low-effort win. The baseline is already clean, so the hook can most likely be added as-is (optionally with a small pyrightconfig.json pinning typeCheckingMode/pythonVersion for stability across basedpyright releases).

Acceptance criteria

• basedpyright hook added, preserving existing config
• (optional) pyrightconfig.json pinning mode/version
• prek run basedpyright --all-files reports 0 errors
• CI green

Context: fleet-wide linting-standardization sweep. Canonical reference config lives in lfreleng-actions/actions-template.