Fix splashscreen theme not updating after theme change

Apply AppCompatDelegate.setDefaultNightMode() when the user changes
the dark theme configuration to ensure the system-level night mode
is synchronized. This makes the splash screen display with the
correct theme on cold start.

Changes:
- SettingsViewModel: Apply night mode immediately when user changes theme
- MainActivity: Apply saved theme config on startup

Fixes #633

app/src/main/kotlin/com/google/samples/apps/nowinandroid/MainActivity.kt

@@ -22,6 +22,7 @@ import androidx.activity.SystemBarStyle
 import androidx.activity.compose.setContent
 import androidx.activity.enableEdgeToEdge
 import androidx.activity.viewModels
+import androidx.appcompat.app.AppCompatDelegate
 import androidx.compose.runtime.CompositionLocalProvider
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
@@ -34,6 +35,7 @@ import androidx.lifecycle.repeatOnLifecycle
 import androidx.metrics.performance.JankStats
 import androidx.tracing.trace
 import com.google.samples.apps.nowinandroid.MainActivityUiState.Loading
+import com.google.samples.apps.nowinandroid.MainActivityUiState.Success
 import com.google.samples.apps.nowinandroid.core.analytics.AnalyticsHelper
 import com.google.samples.apps.nowinandroid.core.analytics.LocalAnalyticsHelper
 import com.google.samples.apps.nowinandroid.core.data.repository.UserNewsResourceRepository
@@ -44,6 +46,7 @@ import com.google.samples.apps.nowinandroid.core.ui.LocalTimeZone
 import com.google.samples.apps.nowinandroid.ui.NiaApp
 import com.google.samples.apps.nowinandroid.ui.rememberNiaAppState
 import com.google.samples.apps.nowinandroid.util.isSystemInDarkTheme
+import com.google.samples.apps.nowinandroid.util.toNightMode
 import dagger.hilt.android.AndroidEntryPoint
 import kotlinx.coroutines.flow.combine
 import kotlinx.coroutines.flow.distinctUntilChanged
@@ -79,6 +82,23 @@ class MainActivity : ComponentActivity() {
         val splashScreen = installSplashScreen()
         super.onCreate(savedInstanceState)
 
+        // Apply the saved dark theme config at startup to ensure the splash screen
+        // uses the correct theme. This addresses issue #633.
+        lifecycleScope.launch {
+            viewModel.uiState
+                .map { state ->
+                    if (state is Success) {
+                        state.userData.darkThemeConfig.toNightMode()
+                    } else {
+                        null
+                    }
+                }
+                .first { it != null } // Only take the first non-null mode
+                .let { mode ->
+                    AppCompatDelegate.setDefaultNightMode(mode)
+                }
+        }
+
         // We keep this as a mutable state, so that we can track changes inside the composition.
         // This allows us to react to dark/light mode changes.
         var themeSettings by mutableStateOf(

feature/settings/impl/src/main/kotlin/com/google/samples/apps/nowinandroid/feature/settings/impl/SettingsViewModel.kt

@@ -16,6 +16,7 @@
 
 package com.google.samples.apps.nowinandroid.feature.settings.impl
 
+import androidx.appcompat.app.AppCompatDelegate
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import com.google.samples.apps.nowinandroid.core.data.repository.UserDataRepository
@@ -62,6 +63,11 @@ class SettingsViewModel @Inject constructor(
     fun updateDarkThemeConfig(darkThemeConfig: DarkThemeConfig) {
         viewModelScope.launch {
             userDataRepository.setDarkThemeConfig(darkThemeConfig)
+            
+            // Apply the night mode at the application level to ensure the splash screen
+            // uses the correct theme on cold start. This addresses issue #633.
+            // Reference: https://developer.android.com/develop/ui/views/theming/darktheme#change-themes
+            AppCompatDelegate.setDefaultNightMode(darkThemeConfig.toNightMode())
         }
     }