[Docs] Warn agents not to leak sensitive context on public GitHub surfaces

[roomote-roomote]

Opened on behalf of Matt Rubens. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

Added an Open source and public surfaces section to the root AGENTS.md so agents treat GitHub and other public surfaces as fully public and avoid leaking customer names, private details, secrets, or internal maintainer discussion into commits, PRs, comments, or related public artifacts.

Why this change was made

This repo is open source, so agent guidance needs an explicit guardrail: private task context must not spill onto public GitHub surfaces.

Impact

No product behavior change. Future agent work should keep customer-specific and internal discussion off public artifacts and prefer private channels for sensitive context.

[roomote-roomote]

No code issues found. See task

Reviewed the docs-only addition of the Open source and public surfaces section in AGENTS.md. The section is well-placed, the guidance is clear and internally consistent, and the markdown is well-formed.

_{Reviewed 2738360}