0fc295d958
Follow-up PR to #5569. Add Keyring Support for Auth Storage in Codex CLI as well as a hybrid mode (default to persisting in keychain but fall back to file when unavailable.) It also refactors out the keyringstore implementation from rmcp-client [here](https://github.com/openai/codex/blob/main/codex-rs/rmcp-client/src/oauth.rs) to a new keyring-store crate. There will be a follow-up that picks the right credential mode depending on the config, instead of hardcoding `AuthCredentialsStoreMode::File`.