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

shared/src/commonMain/kotlin/com/uno/shared/UnoGameScreen.kt

@@ -63,7 +63,7 @@ private class FlyingCardState {
         animatableX = Animatable(fromX)
         animatableY = Animatable(fromY)
         animatableScale = Animatable(0.3f)
-        animatableRotation = Animatable((Math.random() * 60 - 30).toFloat())
+        animatableRotation = Animatable((kotlin.random.Random.nextFloat() * 60 - 30).toFloat())
 
         coroutineScope {
             launch {
@@ -274,6 +274,7 @@ fun UnoGameScreen(
     var previousLastAction by remember { mutableStateOf(state.lastAction) }
     var previousTopCard by remember { mutableStateOf(state.deck.topCard) }
     var lastPlayedByPlayerIndex by remember { mutableIntStateOf(0) }
+    var isDarkMode by remember { mutableStateOf(false) }
 
     val flyingState = rememberFlyingCardState()
 
@@ -317,14 +318,15 @@ fun UnoGameScreen(
         previousLastAction = state.lastAction
     }
 
-    Box(modifier = Modifier.fillMaxSize()) {
-        Column(
-            modifier = Modifier
-                .fillMaxSize()
-                .padding(16.dp),
-            horizontalAlignment = Alignment.CenterHorizontally
-        ) {
-            GameInfoBar(state)
+    UnoTheme(darkTheme = isDarkMode) {
+        Box(modifier = Modifier.fillMaxSize()) {
+            Column(
+                modifier = Modifier
+                    .fillMaxSize()
+                    .padding(16.dp),
+                horizontalAlignment = Alignment.CenterHorizontally
+            ) {
+                GameInfoBar(state, isDarkMode, { isDarkMode = it })
             Spacer(modifier = Modifier.height(12.dp))
             OpponentHands(state)
             Spacer(modifier = Modifier.height(12.dp))
@@ -417,12 +419,13 @@ fun UnoGameScreen(
             }
         )
     }
+    }
 }
 
 // region --- GameInfoBar ---
 
 @Composable
-private fun GameInfoBar(state: GameState) {
+private fun GameInfoBar(state: GameState, isDarkMode: Boolean, onDarkModeToggle: (Boolean) -> Unit) {
     val directionRotation by animateFloatAsState(
         targetValue = if (state.direction == GameDirection.CLOCKWISE) 0f else 180f,
         animationSpec = tween(500, easing = FastOutSlowInEasing),
@@ -462,6 +465,13 @@ private fun GameInfoBar(state: GameState) {
                     )
                 }
             }
+            // Dark mode toggle
+            IconButton(onClick = { onDarkModeToggle(!isDarkMode) }) {
+                Text(
+                    text = if (isDarkMode) "\u2600\uFE0F" else "\uD83C\uDF19",
+                    style = MaterialTheme.typography.bodyLarge
+                )
+            }
         }
     }
 }

shared/src/commonMain/kotlin/com/uno/shared/UnoTheme.kt

@@ -0,0 +1,57 @@
+package com.uno.shared
+
+import androidx.compose.foundation.isSystemInDarkTheme
+import androidx.compose.material3.*
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.graphics.Color
+
+private val LightColorScheme = lightColorScheme(
+    primary = Color(0xFF1976D2),
+    onPrimary = Color.White,
+    primaryContainer = Color(0xFFBBDEFB),
+    onPrimaryContainer = Color(0xFF0D47A1),
+    secondary = Color(0xFFFF6D00),
+    onSecondary = Color.White,
+    secondaryContainer = Color(0xFFFFE0B2),
+    onSecondaryContainer = Color(0xFFE65100),
+    background = Color(0xFFF5F5F5),
+    onBackground = Color(0xFF1C1B1F),
+    surface = Color.White,
+    onSurface = Color(0xFF1C1B1F),
+    surfaceVariant = Color(0xFFE7E0EC),
+    onSurfaceVariant = Color(0xFF49454F),
+    error = Color(0xFFE53935),
+    onError = Color.White,
+)
+
+private val DarkColorScheme = darkColorScheme(
+    primary = Color(0xFF90CAF9),
+    onPrimary = Color(0xFF0D47A1),
+    primaryContainer = Color(0xFF1565C0),
+    onPrimaryContainer = Color(0xFFBBDEFB),
+    secondary = Color(0xFFFFB74D),
+    onSecondary = Color(0xFF3E2723),
+    secondaryContainer = Color(0xFFE65100),
+    onSecondaryContainer = Color(0xFFFFE0B2),
+    background = Color(0xFF121212),
+    onBackground = Color(0xFFE6E1E5),
+    surface = Color(0xFF1E1E1E),
+    onSurface = Color(0xFFE6E1E5),
+    surfaceVariant = Color(0xFF2C2C2C),
+    onSurfaceVariant = Color(0xFFCAC4D0),
+    error = Color(0xFFEF5350),
+    onError = Color(0xFF601010),
+)
+
+@Composable
+fun UnoTheme(
+    darkTheme: Boolean = isSystemInDarkTheme(),
+    content: @Composable () -> Unit
+) {
+    val colorScheme = if (darkTheme) DarkColorScheme else LightColorScheme
+
+    MaterialTheme(
+        colorScheme = colorScheme,
+        content = content
+    )
+}