Eject from Expo (pros and cons)

We're considering ejecting from expo:

Pros
- Use [React Native Firebase](https://rnfirebase.io/) instead of the Firebase Web SDK. React Native Firebase has several features/APIs which we want to use.

Cons
- Using Expo helps onboard new contributors quickly. If we eject, we will likely need some more involved maintenance to keep everything running smoothly for new contributors.

The issue names no files, tests, or entry points; begin by reviewing the existing Expo setup and the linked React Native Firebase documentation. There is no defined implementation or completion criterion yet, so the pros and cons need a decision before work can be scoped.

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