feat: UNO Kotlin Multiplatform app (Android, Desktop, Web)

- Full UNO game logic with AI opponents
- Compose Multiplatform UI with animations
- Shared module (commonMain) with game engine
- Desktop app (Compose Desktop)
- Android app (Compose Multiplatform)
- Web app (Kotlin/Wasm)
- Nix shell for reproducible dev environment

gradle.properties

@@ -0,0 +1,5 @@
+org.gradle.jvmargs=-Xmx2048M -Dfile.encoding=UTF-8 -Dkotlin.daemon.jvm.options="-Xmx2048M"
+kotlin.code.style=official
+android.useAndroidX=true
+android.nonTransitiveRClass=true
+org.gradle.configuration-cache=true