Make RN components fully theme-driven for multi-brand support

Refactor all 18 React Native components from static DTColors imports to
dynamic useDTTheme() context, enabling proper visual differentiation
when switching between DT and Classic brands.

Key changes:
- Replace static DTColors with theme context in all components
- Add shape tokens (bevel/radius) to DTExtendedTheme interface
- Conditionally render SVG bevels (DT) vs borderRadius (Classic)
- Configure fonts per brand (Tektur for DT, system sans-serif for Classic)
- Update buildThemeFromBrand to parse shape and typography tokens
- Fix Metro config for monorepo singleton resolution

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/react-native/src/index.ts

@@ -27,7 +27,7 @@ export { DTThemeProvider, useDTTheme } from './theme/DTThemeProvider';
 
 // Shared utilities
 export type { DTVariant } from './utils/variantColors';
-export { variantColorMap, getVariantColor } from './utils/variantColors';
+export { getVariantColor } from './utils/variantColors';
 export { buildBeveledRectPath } from './utils/bevelPaths';
 export { useComponentLayout } from './utils/useComponentLayout';