Migrate Empower Plant to Expo and showcase Expo-related features

[alwx]

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

[linear-code]

RN-717

[sentry-pierre]

The repo already has a minimal Expo sample at samples/expo/. Most items on this list are already active there: expoContextIntegration, expoUpdatesListenerIntegration, and expoRouterIntegration are included by default; wrapExpoRouter and build-time autoWrapExpoRouterErrorBoundary are wired up too. The gaps are wrapExpoImage, wrapExpoAsset, and the native-early init path (sentry.options.json + RNSentrySDK.init()).