[misc] add AGENTS.md file

Add the first version of the agents.md file and update the contributing guide to reflect expectations.

the CLAUDE.md redirects agents to AGENTS.md

CONTRIBUTING.md

@@ -66,11 +66,41 @@ Typical bug fixes, internal refactors, documentation updates, and tests do not
 need a design discussion, but should still be tied to an issue so the work is
 visible and nobody duplicates it.
 
+### Using AI coding agents
+
+We have no policy for or against using an AI agent to write NetBird code. That
+choice is yours, and we are not going to interrogate anyone about their tools.
+
+What we do have is a lot of incoming contributions that were plainly drafted with
+one, and enough experience reviewing them to see the same avoidable problems
+again and again: no ticket behind the change, a diff far too large to review, a
+description longer than the code it describes, an approach that was never going
+to be accepted, and an author who cannot answer questions about their own PR.
+None of that is caused by the tooling — it is what happens when a tool is pointed
+at a repository whose expectations it has never been told.
+
+So rather than a rule, there is a guide. [AGENTS.md](AGENTS.md) restates the
+expectations from this document in the form agents read automatically
+(`CLAUDE.md` points to it), so pointing your tool at the repository is usually
+enough. Among other things it tells the agent to ask you for the
+discussion or issue before drafting a PR, to keep the change small and
+single-purpose, to run the tests locally, to use this repository's PR template
+and title tags, and to write a description a reviewer can get through.
+
+The guardrails are the point, and they are the same ones we apply to everyone: an
+agreed ticket, a change you have actually run, a diff small enough to review with
+care, and an author who can explain it. Whatever wrote the diff, you are its
+author — you own every line you submit and the consequences of opening a PR with it.
+
+We reserve the right to consider if it is worth to maintain the contribution and to ensure 
+that what is merged aligns with our security standards and design expectations.
+
 ## Contents
 
 - [Contributing to NetBird](#contributing-to-netbird)
     - [Ticket first, PR second](#ticket-first-pr-second)
         - [High-risk areas](#high-risk-areas)
+        - [Using AI coding agents](#using-ai-coding-agents)
     - [Contents](#contents)
     - [Code of conduct](#code-of-conduct)
     - [Directory structure](#directory-structure)