VS Code extension webview goes blank when chatgpt.localeOverride value is not valid

What version of the IDE extension are you using?

26.5422.71525

What subscription do you have?

plus

Which IDE are you using?

vscode

What platform is your computer?

Microsoft Windows NT 10.0.26200.0 x64

What issue are you seeing?

The Codex VS Code extension webview becomes blank after the loading spinner when chatgpt.localeOverride is set to Simplified Chinese.

The DevTools console shows that the value is passed to Intl.NumberFormat.supportedLocalesOf, which throws a RangeError because simplified chinese is not a valid BCP 47 language tag.

What steps can reproduce the bug?

1. Open VS Code on Windows.
2. Install / enable the Codex extension.
3. Open VS Code settings.json.
4. Add:

{
  "chatgpt.localeOverride": "Simplified Chinese"
}
````

5. Reload the VS Code window.
6. Open the Codex panel.

### What is the expected behavior?

The extension should either:

* validate the setting and show a visible configuration error,
* map common locale names such as `Simplified Chinese` to `zh-CN`,
* or safely fall back to the default locale.

The webview should not become blank.

### Additional information

DevTools console error:

```text
lib-WdAB31PD.js:26 Uncaught RangeError: Invalid language tag: simplified chinese
    at NumberFormat.supportedLocalesOf (<anonymous>)
    at It (lib-WdAB31PD.js:26:207)
    at Q (lib-WdAB31PD.js:26:6974)
    at t.getDerivedStateFromProps (lib-WdAB31PD.js:26:8588)
    at Fs (index-SwN8SOG1.js:9:63089)
    at uc (index-SwN8SOG1.js:9:73005)
    at Tc (index-SwN8SOG1.js:9:80522)
    at Mu (index-SwN8SOG1.js:9:116007)
    at ku (index-SwN8SOG1.js:9:115054)
    at Ou (index-SwN8SOG1.js:9:114887)
    at gu (index-SwN8SOG1.js:9:111714)
    at ud (index-SwN8SOG1.js:9:123492)
    at ad (index-SwN8SOG1.js:9:122046)
    at sd (index-SwN8SOG1.js:9:122320)
    at index-SwN8SOG1.js:9:123546