`SpawnedCodexAppServerClient.initialize()` passes `this.options.env` to
`spawn()`, but no caller ever sets `env` in options. In Node.js, passing
`undefined` for `env` gives the child process **no** environment variables,
breaking any model provider that relies on env vars (e.g. DATABRICKS_TOKEN).
Fall back to `process.env` when `this.options.env` is not set, matching the
existing pattern in `broker-lifecycle.mjs` and `codex-companion.mjs`.
Co-authored-by: Isaac
Co-authored-by: Bhuvanesh Sridharan <bhuvanesh.sridharan@databricks.com>