docs: document product team access

[kavatana]

What changed

• documents the four active product-team slugs;
• updates onboarding to assign members through teams rather than direct repo grants;
• explains that team access and CODEOWNERS work together for automatic review.

Why

The organization now has three active members and product-scoped teams. The public operating guide should match the actual GitHub access model so a new teammate or agent receives accurate instructions.

Verification

• python3 scripts/verify_profile.py
• git diff --check

AI involvement and human review

Codex prepared this documentation update after creating and verifying the teams. A CHNAI LAB member should confirm the team-to-product mapping before marking ready and merging.

Risk and rollback

Documentation only. Revert commit e244662 to roll back.