[Feature Request] Add Chinese (zh-CN) language support in settings

Problem

Codex desktop app (Windows MSIX from Microsoft Store) does not provide a language switching option. The system locale is zh-CN, and the app package already contains Chinese locale files (app/locales/zh-CN.pak) and Chinese translation strings in the asar bundle (react-intl messages for zh-TW are visible in the code). However, the UI stays in English with no way to change it.

Current behavior

• App always displays in English
• No language option in Settings
• DevTools are blocked (F12/Ctrl+Shift+I disabled in MSIX build)

Expected behavior

• Option to switch UI language to Chinese (zh-CN) in Settings > General > Language
• Or auto-detect system locale and switch accordingly

Environment

• OS: Windows (zh-CN)
• Codex version: installed from Microsoft Store (MSIX)
• System language: Simplified Chinese

Additional context

The translations seem to already exist in the codebase - the native menu locales include zh-CN and zh-TW, and the React app bundle contains Chinese UI string messages. It would be a matter of exposing the language picker in Settings and wiring it to the existing i18n (react-intl/formatjs) infrastructure.