fix(boilerplate): main entry point

[frankcalise]

Please verify the following:

• yarn test jest tests pass with new tests, if relevant
• yarn lint eslint checks pass with new code, if relevant
• yarn format:check prettier checks pass with new code, if relevant
• README.md (or relevant documentation) has been updated with your changes
• If this affects functionality there aren't tests for, I manually tested it, including by generating a new app locally if needed (see docs).

Describe your PR

• Closes Ignite expo mobile app in Yarn monorepo stuck in splash screen #2875
• We had an old main value from the Expo Go days and while it worked in standard repos, it would not work properly in a monorepo out of the box. This fixes that.

Test Plan

Reproduction

• Follow [https://ignitecookbook.com/docs/recipes/SettingUpYarnMonorepo](Setting Up Yarn Monorepo] cookbook recipe
  • Note: in doing so I had to make some touch ups to the recipe, which can be found in this PR if not yet published
• Observe the Before screenshot below

Validation with plain Expo

• Follow [https://docs.expo.dev/guides/monorepos/#create-our-first-app](monorepo guide)
• Upon generating the app template, make sure to generate the app via npx create-expo-app@latest --template react-navigation/template to get a proper React Navigation template - otherwise expo-router will be used (which won't have this problem)

Updating Ignite

• From the error state, modify the following:
  1. package.json, key main to App.tsx (an existing file)
  2. modify the contents of App.tsx to the following:

import "@expo/metro-runtime"
import { registerRootComponent } from "expo"
import * as SplashScreen from "expo-splash-screen"
import App from "@/app"

SplashScreen.preventAutoHideAsync()

function IgniteApp() {
  return <App hideSplashScreen={SplashScreen.hideAsync} />
}

registerRootComponent(IgniteApp)

• Observe the After screenshot after running the app again

Screenshots (if applicable)

Before	After

[flexbox]

LGTM 🙌

[infinitered-circleci]

🎉 This PR is included in version 10.1.2 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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