Fix white screen on in-app back from game, add controller diagram

Guard game exit to prevent double-pop and pause core before navigating.
Replace flat button chip grid with visual gamepad layout in test screen.

app/src/main/java/com/lazy/emulate/ui/screens/game/GameScreen.kt

@@ -90,6 +90,15 @@ fun GameScreen(
     var displayMode by remember { mutableStateOf(preferencesManager.displayMode) }
     var loadError by remember { mutableStateOf<String?>(null) }
     var surfaceViewRef by remember { mutableStateOf<SurfaceView?>(null) }
+    var isExiting by remember { mutableStateOf(false) }
+
+    val safeBack: () -> Unit = {
+        if (!isExiting) {
+            isExiting = true
+            core?.pause()
+            onBack()
+        }
+    }
 
     // Launch menu: shown before emulation starts if saves exist
     var showLaunchMenu by remember { mutableStateOf(true) }
@@ -172,7 +181,7 @@ fun GameScreen(
                     pendingLoadSlot = -1
                     showLaunchMenu = false
                 },
-                onBack = onBack
+                onBack = safeBack
             )
         } else {
             // Emulation surface
@@ -240,7 +249,7 @@ fun GameScreen(
             // HUD controls (hidden when game menu is open)
             if (!showGameMenu) {
                 IconButton(
-                    onClick = onBack,
+                    onClick = safeBack,
                     modifier = Modifier
                         .align(Alignment.TopStart)
                         .padding(8.dp)