Add GitHub Copilot instructions for repository

[Copilot]

Configures GitHub Copilot coding agent with repository-specific context per best practices.

Changes

• Added .github/copilot-instructions.md with:
  • Magento 2 module context (PHP 8.3+, requires 2.4.7+)
  • Coding standards: Magento Coding Standards, PSR-4, strict typing with declare(strict_types=1), constructor property promotion with readonly
  • Code formatting: 4-space indentation, 80-char lines, PascalCase classes, camelCase methods
  • Build validation: PHPCS with Magento2 standard
  • Git conventions: #<issue> - <message> commit format
  • Project structure: Command patterns, service layer, theme builder interface implementations
  • Domain guidance: Theme builders in Service/ThemeBuilder/, Magento DI patterns, CLI command shortcodes

This enables Copilot to generate code consistent with project conventions and understand the Magento 2 module architecture.

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 #47

---

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[Copilot]

Pull request overview

This PR adds GitHub Copilot instructions to configure the coding agent with repository-specific context for the MageForge project, following GitHub's best practices for Copilot integration.

Key Changes

• Added comprehensive .github/copilot-instructions.md file with Magento 2 module context
• Documented coding standards including PHP 8.3+ requirements, PSR-4, strict typing, and constructor property promotion
• Included project-specific conventions for Git workflow, CLI command patterns, and theme builder architecture

[Copilot]

The command example shows installing magento-coding-standard to /tmp/ which is a temporary directory that may be cleared on system restart. Consider documenting a more permanent installation location or using a project-local installation method via composer require-dev for better reproducibility.

Suggested change

	composer create-project magento/magento-coding-standard --stability=dev /tmp/magento-coding-standard
	/tmp/magento-coding-standard/vendor/bin/phpcs -p -s --standard=Magento2 src/
	composer require --dev magento/magento-coding-standard
	vendor/bin/phpcs -p -s --standard=Magento2 src/

[Copilot]

The formatting example shows -p -s flags for phpcs but doesn't explain what these flags do. Consider adding a brief explanation (e.g., "-p shows progress, -s shows sniff codes") to make the documentation more helpful for contributors who may not be familiar with PHPCS.

Suggested change

```

Note: The -p flag shows progress, and the -s flag shows sniff codes in the output.