Skill: Expo/React Native + Electric integration

## Context

React Native with Expo is a supported platform for Electric + TanStack DB. AGENTS.md mentions `react-native-random-uuid` as a requirement, but the full setup story is more involved.

## Scope

Create an `electric-expo` skill covering:

1. **Prerequisites** — `react-native-random-uuid` import in entry point, polyfills needed
2. **Proxy setup** — Mobile app → your API server → Electric (different from web proxy patterns)
3. **Offline behavior** — How Electric's HTTP-based sync behaves when mobile network drops
4. **Background/foreground transitions** — Visibility detection, reconnection on app resume
5. **TanStack DB integration** — Collections with React Native-specific considerations
6. **Expo-specific setup** — Metro bundler config, Expo Router API routes
7. **Testing on device vs simulator** — Network configuration, localhost vs LAN IP

## Source

Identified during domain discovery skill test run. Maintainer confirmed React Native warrants standalone skill due to integration complexity.