Reverts c61977c. The live listing needed no codex CLI on the user's
machine — kigi issued the request itself and `client_version` was a
compiled-in string — but the project keeps the catalog in the binary, so
the fetch path, the `OpenaiCodex` listing dialect, its parser and the
pinned client version are gone again, and the codex `User-Agent` returns
to its previous value.
The models.dev provider rename `kimi-for-coding` → `kimi-code-plan-cn`
rode in the same commit and stays: the regenerated snapshot ships under
the new id.