Cache flags + env `CPA_*` (`--offline/--no-cache/--cache-dir/--pin/--refresh/--strict-version`)

[ulises-jeremias]

Summary

Wire cache/refresh/version flags to core + env vars.

CNA mapping

CNA: CNA_* env vars and matching flags.

Acceptance criteria

• Env names use CPA_ prefix per parity matrix
• Flags set env/core options correctly
• Tests cover offline and no-cache

Blocked by

none

Blocks

none

Reference

Parity matrix (workspace): knowledge/create-python-app-parity-matrix.md
Reference repo: https://github.com/Create-Node-App/create-node-app

Parent epic

#5