Fixed login failure with API key in IDE extension when a .codex directory doesn't exist (#4258)

This addresses bug #4092

Testing:
* Confirmed error occurs prior to fix if logging in using API key and no
`~/.codex` directory exists
* Confirmed after fix that `~/.codex` directory is properly created and
error doesn't occur

codex-rs/core/src/auth.rs

@@ -267,6 +267,9 @@ pub fn try_read_auth_json(auth_file: &Path) -> std::io::Result<AuthDotJson> {
 }
 
 pub fn write_auth_json(auth_file: &Path, auth_dot_json: &AuthDotJson) -> std::io::Result<()> {
+    if let Some(parent) = auth_file.parent() {
+        std::fs::create_dir_all(parent)?;
+    }
     let json_data = serde_json::to_string_pretty(auth_dot_json)?;
     let mut options = OpenOptions::new();
     options.truncate(true).write(true).create(true);