feat(skills): add wellarchitected.github.com content to iac-terraform-modules-eng

## Summary

Add references and patterns from https://wellarchitected.github.com to the `iac-terraform-modules-eng` skill.

## Rationale

The GitHub Well-Architected framework provides best practices for repository structure, CI/CD, and collaboration patterns that complement Terraform module development. Currently, this skill references AWS/Azure Well-Architected Frameworks but not the GitHub-specific framework.

## Scope

- Add wellarchitected.github.com as a reference alongside existing AWS/Azure Well-Architected references
- Incorporate GitHub-specific patterns for module repository structure
- Add guidance on module CI/CD, testing workflows, and release automation per the framework

## Related Skills

This is part of a broader effort to add wellarchitected.github.com content to:
- cicd-github-actions-dev
- cicd-github-actions-ops
- github-actions-dev
- github-app-dev
- iac-terraform-modules-eng (this issue)
- iac-terraform-orchestration-ops