docs: introduce `AGENTS.md` to define rules for AI-Assisted contributions

[wmontwe]

We are seeing an increasing number of AI-assisted and AI-generated contributions to the project. While such contributions can be valuable, they need to follow clear project rules around architecture, quality, privacy, security, and licensing.

This issue proposes adopting the open AGENTS.md standard (https://agents.md/) and adding an AGENTS.md file at the repository root to define expectations for AI agents and contributors using AI tools.

The goals are to:

• Ensure AI-assisted changes respect existing architecture and module boundaries
• Require proper testing, linting, and documentation
• Prevent introduction of telemetry, insecure patterns, or unnecessary dependencies
• Clarify contributor responsibility, including disclosure of AI assistance and licensing compliance

AI-assisted contributions may be accepted if they meet the same quality, security, and review standards as any other contribution.