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

desktopApp/src/jvmMain/kotlin/com/uno/desktop/Main.kt

@@ -13,6 +13,7 @@ import androidx.compose.ui.window.application
 import com.uno.game.GameEngine
 import com.uno.game.model.*
 import com.uno.shared.UnoGameScreen
+import com.uno.shared.UnoTheme
 import kotlinx.coroutines.delay
 
 fun main() = application {
@@ -49,31 +50,33 @@ fun UnoDesktopApp() {
         }
     }
 
-    if (!gameStarted) {
-        DesktopStartScreen(onStartGame = { playerCount ->
-            gameState = engine.startGame(playerCount)
-            gameStarted = true
-        })
-    } else {
-        UnoGameScreen(
-            state = gameState,
-            onPlayCard = { card, color ->
-                gameState = engine.playCard(gameState, 0, card, color)
-            },
-            onDrawCard = {
-                gameState = engine.drawCard(gameState, 0)
-            },
-            onCallUno = { gameState = engine.callUno(gameState, 0) }
-        )
-
-        if (gameState.isFinished) {
-            DesktopGameOverScreen(
-                winner = gameState.winner,
-                onPlayAgain = {
-                    gameState = engine.startGame()
-                    gameStarted = false
-                }
+    UnoTheme {
+        if (!gameStarted) {
+            DesktopStartScreen(onStartGame = { playerCount ->
+                gameState = engine.startGame(playerCount)
+                gameStarted = true
+            })
+        } else {
+            UnoGameScreen(
+                state = gameState,
+                onPlayCard = { card, color ->
+                    gameState = engine.playCard(gameState, 0, card, color)
+                },
+                onDrawCard = {
+                    gameState = engine.drawCard(gameState, 0)
+                },
+                onCallUno = { gameState = engine.callUno(gameState, 0) }
             )
+
+            if (gameState.isFinished) {
+                DesktopGameOverScreen(
+                    winner = gameState.winner,
+                    onPlayAgain = {
+                        gameState = engine.startGame()
+                        gameStarted = false
+                    }
+                )
+            }
         }
     }
 }