[P2] Expand ownership documentation beyond CODEOWNERS

[Calebux]

Summary

CODEOWNERS alone does not explain who owns product, infra, docs, or incident response for each surface.

Scope

• Area: governance
• Priority: P2
• Backlog ID: #116

Acceptance Criteria

• Ownership matrix includes engineering and product responsibilities.
• Escalation path is documented.
• Major systems list primary and backup owners.

Implementation Notes

• Keep the implementation aligned with current architecture decisions and security constraints in this repo.
• Include tests for changed behavior and update docs where relevant.

Definition of Done

• Acceptance criteria met
• Tests added/updated and passing
• Documentation updated
• No security regressions introduced

Links

• Backlog source: docs/repo-issue-backlog-2026-05.md