Add ThemeProvider.native.tsx (Metro resolves it over the web file): applies the theme StyleX styles to a flex-column container instead of display:contents + a fixed portal mount (neither exists on RN), and exports it from the native barrel. Verified on an iOS sim — theme='light' flips DS leaves (Input, Badge, Button) from base/dark to light. Web build/typecheck unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>