Set up Copilot instructions

[Copilot]

Adds .github/copilot-instructions.md to provide GitHub Copilot with repository-specific context and conventions.

The instructions file covers:

• Development environment: uv for package management, Python 3.10-3.12
• Code style: ruff formatter/linter, pre-commit hooks, mypy type checking, MPL-2.0 license headers required
• Architecture patterns: BzCleaner base class for rules, Jinja2 templates for emails/comments, Bugzilla REST API via libmozdata
• Testing: unittest framework, coverage tracking, mock data in tests/mocks/
• Common workflows: Adding rules, dry-run patterns, database migrations with Alembic
• Pitfalls: Never commit configs/config.json (secrets), always dry-run first, respect normal_changes_max limits

This enables Copilot to generate code that follows project conventions and understands the rules system architecture.

Checklist

• Type annotations added to new functions
• Docs added to functions touched in main classes
• Dry-run produced the expected results
• The to-be-announced tag added if this is worth announcing

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)
  • Triggering command: /usr/bin/curl curl -L REDACTED (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 #2799

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💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.