Migrate Empower Plant to Expo and showcase Expo-related features

Empower Plant runs on bare React Native. Expo is the default for new RN apps now, and we don't have a demo covering the Expo-specific pieces of the SDK.

Things this would let us show off:

* `expoRouterIntegration()` — navigation spans with deep-link correlation and dynamic route params
* `expoContextIntegration()` + `expoUpdatesListenerIntegration()` — EAS Build metadata and OTA update events as breadcrumbs/tags
* `wrapExpoImage()` / `wrapExpoAsset()` — spans around Image.prefetch, Asset.loadAsync
* `sentry.options.json` + `RNSentrySDK.init()` for native-early init (matters more on EAS where you don't own the native side)
* `wrapExpoRouterErrorBoundary()` and the build-time auto-wrap variant