Add Copilot instructions for repository standards and conventions

[Copilot]

Configures .github/copilot-instructions.md to guide AI coding agents on project-specific requirements that aren't readily inferrable from code inspection.

Key Directives

Quality Gates

• PHPStan max level compliance (zero errors)
• Symfony coding standards via PHP-CS-Fixer
• Strict typing (declare(strict_types=1)) in all files

Development Workflow

composer quality-check  # Runs Rector, CS-Fixer, PHPStan, PHPUnit
composer cs-fix         # Auto-format code
composer phpstan        # Static analysis
composer test          # PHPUnit tests

Domain Context

• UN/EDIFACT D23B standard library for CDAR messages
• Models auto-generated from UN/CEFACT XSD schemas
• Namespace: TiimePDP\CrossDomainAcknowledgementAndResponse
• Architecture: Codelist, Enum, QualifiedDataType, UnqualifiedDataType, RABIE entities

Critical Constraints

• GPL-3.0-or-later license (all modifications must preserve)
• Backward compatibility required (library consumers)
• No modification of auto-generated models without XSD regeneration

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 #9

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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.