fix(expo-template): use development build instead of Expo Go

[oleksandrzavarzin-callstack]

PR Description

Bug fix for @bottom-tabs/expo-template. A scaffolded app couldn't be run with the scripts the template ships:

• Scripts targeted Expo Go. Expo Go only bundles Expo's own native modules, so it can never load react-native-bottom-tabs.
  expo start --android / --ios → expo run:android / expo run:ios, and start → expo start --dev-client.
• README advertised Expo Go as a supported way to run. Rewritten around development builds.
• App identifiers were unset. Prebuild silently substitutes com.placeholder.appid for both platforms, so every scaffolded app shares one package name. Added com.example.nativetabs placeholders to app.json plus a README note to change them.
• gitignore was missing /android and /ios, leaving prebuild output untracked but not ignored.

Scripts, config, docs and a patch changeset only - no library changes.

How to test?

Scaffold from the template on this branch, as create-expo-app would:

yarn workspace @bottom-tabs/expo-template pack --out /tmp/expo-template.tgz
npx create-expo-app@latest /tmp/tpl --template /tmp/expo-template.tgz
cd /tmp/tpl

• npm run android / npm run ios build and install a development build (previously opened Expo Go).
• npm start waits for a development build instead of offering Expo Go.
• grep applicationId android/app/build.gradle → com.example.nativetabs.
• git init -q . && git add -A && git check-ignore -v android ios → both ignored.

Screenshots

Not applicable - no runtime or UI change.