Add community skill: project-coding-companion (prompt coaching + implementation)

Hi! I built an open-source skill that coaches users to write better
coding prompts before implementing code changes.

Key features:
- Evaluates prompts against 5 dimensions (context, intent, scope,
constraints, acceptance criteria)
- Coaches with targeted questions + "Why this matters" explanations
- Respects conversation context (no re-asking)
- Structured workflow: evaluate → coach → plan → implement → review
- Also ships as .cursorrules and AGENTS.md

Repo: https://github.com/rgranet/project-coding-companion-skill
License: MIT

Would you be open to including this in the community skills directory?
Happy to submit a PR in whatever format you prefer.