Add custom Copilot instructions

[juan-arias]

Proposed changes

This pull request adds a new documentation file, .github/copilot-instructions.md, which provides comprehensive instructions for working with the MSAL iOS/macOS SDK. The document covers code style guidelines, build and test commands, project architecture, and validation steps to help contributors and Copilot understand the repository's structure and workflows. This addition is aimed at improving onboarding, consistency, and automation support.

Documentation improvements:

• Added .github/copilot-instructions.md with high-level details about the MSAL iOS/macOS SDK, including supported platforms, languages, dependencies, and build system.
• Provided explicit code style guidelines and referenced the location of the style rules.
• Documented build, test, lint, and clean commands using the build.py script, including available targets and prerequisites.
• Explained project directory layout, architecture, and key configuration files for easier navigation and understanding.
• Listed validation steps and CI pipeline details to ensure code quality and consistency before submitting changes.

Type of change

• Feature work
• Bug fix
• Documentation
• Engineering change
• Test
• Logging/Telemetry

Risk

• High – Errors could cause MAJOR regression of many scenarios. (Example: new large features or high level infrastructure changes)
• Medium – Errors could cause regression of 1 or more scenarios. (Example: somewhat complex bug fixes, small new features)
• Small – No issues are expected. (Example: Very small bug fixes, string changes, or configuration settings changes)

Additional information

[Copilot]

Pull request overview

This pull request adds comprehensive Copilot instructions for the MSAL iOS/macOS SDK repository. The document aims to provide guidance on code style, build commands, project architecture, and validation steps to support contributors and AI assistance.

Key Changes:

• Added .github/copilot-instructions.md with SDK overview, supported platforms, and dependencies
• Documented build system usage via build.py script
• Outlined project directory structure and key configuration files

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💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.