markdownlint + shellcheck workflows

[ulises-jeremias]

Summary

Port markdown and shell lint workflows.

CNA mapping

CNA: markdownlint.yml, shellcheck.yml.

Acceptance criteria

• Workflows present and green on empty/docs-only changes
• Scheduled runs optional like CNA

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

#7