Evaluate Codex plugin support for CodeGuard

[thomas-bartlett]

Summary

Evaluate whether Project CodeGuard should provide a Codex plugin distribution, similar to the existing Claude Code plugin path.

Context

Codex supports plugins:
https://developers.openai.com/codex/plugins

This issue tracks whether a CodeGuard plugin would make installation and updates easier for Codex users.

Questions

• Should CodeGuard provide a Codex plugin?
• What should the first version include?
• Should this be the preferred Codex install path or an optional path?
• How should this relate to Emit codeguard-reviewer subagent for Codex #68 and Design a default CodeGuard install CLI #85?

Acceptance Criteria

• Recommendation is documented: build, defer, or do not pursue.
• If recommended, first-version scope is defined.
• Follow-up implementation work can be split into focused issues or PRs.