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

shared/build.gradle.kts

@@ -0,0 +1,44 @@
+plugins {
+    alias(libs.plugins.kotlinMultiplatform)
+    alias(libs.plugins.androidLibrary)
+    alias(libs.plugins.composeMultiplatform)
+    alias(libs.plugins.composeCompiler)
+    alias(libs.plugins.kotlinSerialization)
+}
+
+@OptIn(org.jetbrains.kotlin.gradle.ExperimentalWasmDsl::class)
+kotlin {
+    androidTarget {
+        compilerOptions {
+            jvmTarget.set(org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17)
+        }
+    }
+
+    jvm()
+
+    wasmJs {
+        browser()
+    }
+
+    sourceSets {
+        commonMain.dependencies {
+            implementation(compose.runtime)
+            implementation(compose.foundation)
+            implementation(compose.material3)
+            implementation(libs.kotlinx.serialization.json)
+            implementation(libs.kotlinx.coroutines.core)
+        }
+    }
+}
+
+android {
+    namespace = "com.uno.shared"
+    compileSdk = 35
+    defaultConfig {
+        minSdk = 26
+    }
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_17
+        targetCompatibility = JavaVersion.VERSION_17
+    }
+}