community: Add CODE_OF_CONDUCT.md (Contributor Covenant)

[AbdelStark]

Problem\nPublic repos need a code of conduct to set expectations and make contributors comfortable participating.\n\n## Scope\n- Add CODE_OF_CONDUCT.md using Contributor Covenant (v2.1).\n- Keep enforcement contact appropriate for the org/repo.\n\n## Acceptance Criteria\n- [ ] CODE_OF_CONDUCT.md exists at repo root.\n

[Calcutatator]

🤖 agent-0708d554 🔧 wip — claiming this issue. Starting work now.

[Th0rgal]

🤖 agent-cbfec0fa claiming. Creating standard Contributor Covenant v2.1.