feature: show onboarding as a modal on large screens, add close functionality

shared/src/commonMain/kotlin/bzh/ajaury/chombev/App.kt

@@ -10,7 +10,10 @@ import androidx.compose.runtime.Composable
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateListOf
 import androidx.compose.runtime.saveable.rememberSerializable
+import androidx.compose.ui.platform.LocalDensity
+import androidx.compose.ui.platform.LocalWindowInfo
 import androidx.compose.ui.tooling.preview.Preview
+import androidx.compose.ui.unit.dp
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.navigation3.runtime.NavEntry
 import androidx.navigation3.runtime.metadata
@@ -35,6 +38,9 @@ import org.koin.compose.viewmodel.koinViewModel
 import org.koin.dsl.koinConfiguration
 import org.koin.dsl.module
 
+private val WIDE_WINDOW_MIN_WIDTH = 840.dp
+private val WIDE_WINDOW_MIN_HEIGHT = 600.dp
+
 val appModule = module {
     includes(
         loggingModule,
@@ -59,21 +65,32 @@ fun App() {
             val onboardingViewModel: OnboardingViewModel = koinViewModel()
             val onboardingUiState by onboardingViewModel.uiState.collectAsStateWithLifecycle()
 
-            when (onboardingUiState.isCompleted) {
-                // The persisted flag is still being read: render nothing rather than flashing
-                // either screen.
-                null -> Unit
+            val showOnboardingAsDialog = isWideWindow()
 
-                // First launch: onboarding replaces the whole UI. Completing it flips the persisted
-                // flag, which switches to the main content automatically.
-                false -> OnboardingScreen()
+            val isOnboardingVisible = onboardingUiState.isCompleted == false
+            val isMainContentVisible = onboardingUiState.isCompleted == true ||
+                (isOnboardingVisible && showOnboardingAsDialog)
 
-                true -> MainNavigation(darkTheme = darkTheme)
+            if (isMainContentVisible) {
+                MainNavigation(darkTheme = darkTheme)
+            }
+
+            if (isOnboardingVisible) {
+                OnboardingScreen(showAsDialog = showOnboardingAsDialog)
             }
         }
     }
 }
 
+@Composable
+private fun isWideWindow(): Boolean {
+    val containerSize = LocalWindowInfo.current.containerSize
+    return with(LocalDensity.current) {
+        containerSize.width.toDp() >= WIDE_WINDOW_MIN_WIDTH &&
+            containerSize.height.toDp() >= WIDE_WINDOW_MIN_HEIGHT
+    }
+}
+
 @Composable
 private fun MainNavigation(darkTheme: Boolean) {
     val serializer = SnapshotStateListSerializer<Route>()