Satori's Font.lang needs BCP-47, not ISO-639

Spent 60 seconds of build time getting the runtime crash Invalid value for props 'lang': 'ar' while generating Arabic OG cards via Satori. The Font config takes an optional lang, but it wants BCP-47 tags - ar-AR, ja-JP, zh-CN - not ISO-639 shorts like ar or ja.

Fix: { name: 'IBM Plex Sans Arabic', data: buf, weight: 400, style: 'normal', lang: 'ar-AR' }.

The error message lists the valid enum values, so the fix is obvious once it crashes. But there’s no validation at build time, which means you only find out during the first render pass.