ci: run structured codex review (#134)

## Summary

- replace the connector-comment parser with an OpenAI Codex structured
review job
- publish structured findings as GitHub review comments, using
suggestion fences when Codex returns an exact replacement
- keep the existing required check name as a compatibility job that
mirrors the structured review result

## Checks

- `nix run nixpkgs#actionlint --
.github/workflows/codex-review-gate.yml`
- extracted publisher Python compiles with `python -m py_compile`
- `git diff --check`
- `nix run .#lint`

Co-authored-by: Codex <codex@openai.com>

Author: andrewgazelka