feat: EAS build config for Android APK + BUILD.md (FIBEROPS-210)

- Add versionCode: 1 to app.json android section
- Add preview-local build profile to eas.json (local Gradle build)
- Add build:android:apk and build:android:local npm scripts
- Add BUILD.md documenting EAS cloud and local build instructions

package.json

@@ -6,7 +6,9 @@
     "start": "expo start",
     "android": "expo start --android",
     "ios": "expo start --ios",
-    "web": "expo start --web"
+    "web": "expo start --web",
+    "build:android:apk": "eas build --profile preview --platform android --non-interactive",
+    "build:android:local": "eas build --local --profile preview --platform android"
   },
   "dependencies": {
     "@react-native-async-storage/async-storage": "2.2.0",