docs: Add CODE_OF_CONDUCT.md #229

[Docs] Add CODE_OF_CONDUCT.md

Summary

Add a standard Code of Conduct (e.g. Contributor Covenant) to the repo root.

Why this matters

Sets clear behavioral expectations for a growing contributor base and is a standard signal of a well-run open-source project.

Acceptance criteria

• CODE_OF_CONDUCT.md added at repo root
• Includes a contact/enforcement point
• Linked from README.md or CONTRIBUTING.md

Technical context

None — this is a standalone docs addition.