[js_repl] paths for node module resolution can be specified for js_repl (#11944)

# External (non-OpenAI) Pull Request Requirements

In `js_repl` mode, module resolution currently starts from
`js_repl_kernel.js`, which is written to a per-kernel temp dir. This
effectively means that bare imports will not resolve.

This PR adds a new config option, `js_repl_node_module_dirs`, which is a
list of dirs that are used (in order) to resolve a bare import. If none
of those work, the current working directory of the thread is used.

For example:
```toml
js_repl_node_module_dirs = [
    "/path/to/node_modules/",
    "/other/path/to/node_modules/",
]
```

codex-rs/exec/src/lib.rs

@@ -252,6 +252,7 @@ pub async fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> any
         model_provider: model_provider.clone(),
         codex_linux_sandbox_exe,
         js_repl_node_path: None,
+        js_repl_node_module_dirs: None,
         zsh_path: None,
         base_instructions: None,
         developer_instructions: None,