[Docs] Add AGENTS.md file for AI coding agent instructions

[AClerbois]

📖 Description

This PR adds an AGENTS.md file to the root of the repository following the agents.md standard.

What is AGENTS.md?

AGENTS.md is an open format for guiding AI coding agents, used by over 60k open-source projects. It serves as a README for AI agents - a dedicated, predictable place to provide context and instructions to help AI coding agents work effectively on the project.

Purpose

While README.md files are for humans (quick starts, project descriptions, contribution guidelines), AGENTS.md complements this by containing the extra context AI coding agents need:

• Project overview and repository structure
• Build and test commands for the solution
• Code style guidelines (nullable, warnings as errors, etc.)
• PR guidelines and commit message conventions
• Contributing workflow (fork-based model with upstream configuration)
• Security considerations
• Links to additional resources

Compatibility

The AGENTS.md format is compatible with a growing ecosystem of AI coding tools including:

• GitHub Copilot
• OpenAI Codex
• Google Jules
• Cursor
• VS Code
• And many more...

👩‍💻 Reviewer Notes

This is a documentation-only change that adds guidance for AI coding agents working on this repository. No code changes are included.

📑 Test Plan

N/A - Documentation only.

✅ Checklist

General

• I have added tests for my changes.
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.

📚 References

• agents.md standard
• 60k+ examples on GitHub

[Copilot]

Pull request overview

This PR adds an AGENTS.md file following the agents.md standard to provide structured guidance for AI coding agents working on the Microsoft Fluent UI Blazor components library. The file serves as a dedicated resource containing project context, build instructions, coding standards, and contribution workflows specifically tailored for AI agents.

• Adds comprehensive project setup and build instructions
• Documents code style guidelines, test conventions, and PR requirements
• Provides repository structure overview and contribution workflow guidance

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

[AClerbois]

I've addressed the review feedback:

✅ Updated Node.js version from 20.15 LTS to 22.x
✅ Updated Visual Studio version to 2026
✅ Removed --configuration Debug from all build and test commands

@vnbaaij Regarding your question about keeping dev-v5 as default after the next release - the file is indeed targeting v5 and uses dev-v5 branch references. Let me know if this should be adjusted for future compatibility.

[AClerbois]

@vnbaaij & @dvoituron I updated this PR 👍