Enable CodeRabbit for the repo

[Komzpa]

https://www.coderabbit.ai/oss allows free usage for OSS projects, we qualify. This should add an extra pair of mechanical eyes in addition to the codex review. @Soju06 since it's on your account you're the one to click it through if you think it's a good idea. I have been using it for several years and am quite happy with results.

[Soju06]

Sounds good — let's try it. Enabling it under the OSS plan, starting with the default config; if it gets too noisy I'll tune it with a .coderabbit.yaml.

Since this gives us an always-on mechanical reviewer, I'm also retiring the auto-posted @codex review label gate (Codex review labels workflow + label sync script) in a follow-up PR — CodeRabbit takes over that role. Local/manual Codex reviews stay available as an extra tool.

[chatgpt-codex-connector]

To use Codex here, create an environment for this repo.

[Komzpa]

as mentioned in #1763 (comment) @Soju06 I think disabling codex review should be postponed until we observe both systems find same things (they find different things in my experience so I'd rather keep both)