[codex] Add code of conduct

[justinjoy]

Summary

Adds a root CODE_OF_CONDUCT.md that defines expected community behavior for factlog contributors and participants.

Details

The document covers:

• a community pledge and standards for respectful participation
• examples of unacceptable behavior
• reporting guidance for public and sensitive incidents
• maintainer enforcement options and recusal guidance
• attribution to Contributor Covenant 2.1

Impact

This gives contributors and maintainers a clear shared baseline for conduct in project spaces such as issues, pull requests, discussions, and related forums.

Validation

• Reviewed the staged diff before commit.
• No code tests were run because this is a documentation-only change.