Add release build config and Play Store prep

- Add signing config (reads from env vars)
- Enable R8 minification and resource shrinking
- Expand ProGuard rules for Gson
- Update README with build instructions and Play Store checklist

README.md

@@ -185,9 +185,44 @@ curl -s http://192.168.42.1:8765/status | jq -r '"\(.connection.type) \(.connect
 
 ## Building
 
-1. Open in Android Studio
-2. Build > Build APK
-3. Install APK on your phone
+### Debug build
+
+```bash
+./gradlew assembleDebug
+# Output: app/build/outputs/apk/debug/app-debug.apk
+```
+
+### Release build
+
+1. Generate a keystore:
+```bash
+keytool -genkey -v -keystore keystore.jks -keyalg RSA -keysize 2048 -validity 10000 -alias release
+```
+
+2. Build with signing:
+```bash
+export KEYSTORE_PASSWORD="your-password"
+export KEY_ALIAS="release"
+export KEY_PASSWORD="your-key-password"
+./gradlew assembleRelease
+# Output: app/build/outputs/apk/release/app-release.apk
+```
+
+## Play Store Publishing
+
+### Still needed:
+
+- [ ] **App icons** - Replace placeholder icons in `app/src/main/res/mipmap-*` with proper 512x512 adaptive icons
+- [ ] **Privacy policy** - Required URL (app uses location permission)
+- [ ] **Screenshots** - Phone screenshots for Play Store listing
+- [ ] **Feature graphic** - 1024x500 banner image
+- [ ] **Store description** - Short and full descriptions
+
+### Already configured:
+
+- [x] Release signing config
+- [x] ProGuard/R8 minification
+- [x] Target SDK 36 (meets Play Store requirements)
 
 ## License