EAS build config for App Store / Play Store submission

[teslashibe]

Problem

There is no eas.json in the repo. Expo Go works fine for dev and web, but native iOS/Android distribution (TestFlight, Play Store) requires EAS Build.

Solution

Add eas.json with development, preview, and production build profiles. Update the README with the submission checklist.

Implementation

```bash
cd mobile
npm install -g eas-cli
eas build:configure # generates eas.json
```

Add to mobile/eas.json:
```json
{
"cli": { "version": ">= 12.0.0" },
"build": {
"development": {
"developmentClient": true,
"distribution": "internal"
},
"preview": {
"distribution": "internal"
},
"production": {}
},
"submit": {
"production": {}
}
}
```

Add Makefile targets: make build-ios, make build-android, make submit-ios.

Notes

• Each client fork sets their own Apple Team ID and bundle identifier in app.config.ts
• Requires an Expo account and the client's Apple/Google developer credentials