Update Python Security Standards

[sfitz42]

This PR updates the Python coding standards to add package management guidance using uv
and introduces supply-chain security controls via pyproject.toml settings.

Summary of changes:

• New "Package Management" section covering:
  • uv mandated for all project management (dependency resolution, version pinning, virtual environments)
  • pyproject.toml required for all projects
  • Dependency pinning with exact versions (== specifiers)
  • uv.lock must be committed; uv sync --locked in CI
  • Automated dependency checking (Dependabot / uv pip audit)
• Supply-chain security settings added:
  • exclude-newer = "1 week" quarantine window for new packages
  • exclude-newer-package per-package override with verification checklist
• Code block formatting fixed throughout document (indentation removed from fenced blocks)