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

eas.json

@@ -13,6 +13,14 @@
         "buildType": "apk"
       }
     },
+    "preview-local": {
+      "distribution": "internal",
+      "android": {
+        "buildType": "apk",
+        "gradleCommand": ":app:assembleRelease"
+      },
+      "env": {}
+    },
     "production": {
       "autoIncrement": true
     }