[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/core/src/codex.rs

@@ -1327,7 +1327,7 @@ impl Session {
         };
         let js_repl = Arc::new(JsReplHandle::with_node_path(
             config.js_repl_node_path.clone(),
-            config.codex_home.clone(),
+            config.js_repl_node_module_dirs.clone(),
         ));
 
         let prewarm_model_info = models_manager
@@ -7413,7 +7413,7 @@ mod tests {
         };
         let js_repl = Arc::new(JsReplHandle::with_node_path(
             config.js_repl_node_path.clone(),
-            config.codex_home.clone(),
+            config.js_repl_node_module_dirs.clone(),
         ));
 
         let turn_context = Session::make_turn_context(
@@ -7562,7 +7562,7 @@ mod tests {
         };
         let js_repl = Arc::new(JsReplHandle::with_node_path(
             config.js_repl_node_path.clone(),
-            config.codex_home.clone(),
+            config.js_repl_node_module_dirs.clone(),
         ));
 
         let turn_context = Arc::new(Session::make_turn_context(