feat: add dark mode with toggle in top bar

- Created UnoTheme.kt with light/dark color schemes
- Added dark mode toggle (moon/sun icon) in GameInfoBar
- Wrapped all entry points (Desktop, Android, Web) with UnoTheme
- Fixed Web entry point to use CanvasBasedWindow
- Fixed Math.random() for WASM compatibility

androidApp/src/androidMain/kotlin/com/uno/android/MainActivity.kt

@@ -13,6 +13,7 @@ import androidx.compose.ui.unit.dp
 import com.uno.game.GameEngine
 import com.uno.game.model.*
 import com.uno.shared.UnoGameScreen
+import com.uno.shared.UnoTheme
 import kotlinx.coroutines.delay
 
 class MainActivity : ComponentActivity() {
@@ -20,7 +21,7 @@ class MainActivity : ComponentActivity() {
         super.onCreate(savedInstanceState)
         enableEdgeToEdge()
         setContent {
-            MaterialTheme {
+            UnoTheme {
                 Surface(modifier = Modifier.fillMaxSize(), color = MaterialTheme.colorScheme.background) {
                     UnoApp()
                 }