Add contributing guidelines to Copilot instructions

[Copilot]

The repository's Copilot instruction files were missing contribution workflow documentation, which helps AI coding agents understand the project's PR and issue processes.

Changes

Added Section 10 "Contributing Guidelines" to .github/copilot-instructions.md covering:

• Issue Reporting: Requirements for bug reports and feature requests (environment details, reproduction steps, use case explanations)
• Pull Request Process: 7-step workflow from fork to merge, including local testing requirements (pytest, ruff check, mypy)
• Development Workflow: Branch naming conventions (feature/, fix/, docs/), commit message style (present tense), testing and documentation requirements
• Release Process: Semantic versioning, automated PyPI releases via GitHub Actions

Context

The existing instruction files (.github/copilot-instructions.md, AGENTS.md, CLAUDE.md) were already comprehensive with project architecture, code style, testing guidelines, and backend-specific documentation. This addition completes the best practices coverage by documenting the contribution lifecycle.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• gh.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>✨ Set up Copilot instructions</issue_title>
<issue_description>Configure instructions for this repository as documented in Best practices for Copilot coding agent in your repository.

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes ✨ Set up Copilot instructions #332

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.