Enable Codex on Garand-Desktop and Garand-Laptop.
Keep it disabled on the default host.
Add a new `codex.nix` module and import it in the home
configuration. Introduce a shared `skills.nix` module that
downloads Ponytail and Caveman skill files for both
`.agents/skills` and `.codex/skills`. Update Helium to
0.19.3.1 with the correct hash. Remove the obsolete Zed
skills module.
GarandPLG
40421f044c