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

app.json

@@ -22,6 +22,7 @@
         "backgroundColor": "#0891B2"
       },
       "package": "com.fiberops.mobile",
+      "versionCode": 1,
       "permissions": [
         "android.permission.CAMERA",
         "android.permission.RECORD_AUDIO",