Add AGENTS.md at repo root

[tbeaudouin05]

📝 Description

Add AGENTS.md to capture the agent working agreement so everyone—humans or AI assistants—consistently follows the same coding standards, documentation expectations, testing requirements, and the make test gate after any change.

🗣️ Type of Change

• 🐞 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 📖 Documentation update
• ⚡ Code refactoring (no functional changes, no api changes)

🤖 AI Code Generation

• 🤖 Fully AI-generated (100% AI, 0% Human)
• 🛠️ Mostly AI-generated (AI draft, Human verified/modified)
• 👨‍💻 Mostly Human-written (Human lead, AI assisted or none)

🔗 Related Issue

📚 Technical Context (Skip for Docs)

• Reference URL:
• Reasoning: Establishes a single, repo-local policy so contributors (including AI agents) reliably adhere to style, docs updates, unit tests, and running make test after changes.

🧪 Test Environment

• Hardware:
• OS:
• Model/Provider:
• Channels: