fix: use AppCompatActivity for per-app locale support

AppCompatDelegate.setApplicationLocales() requires an AppCompatActivity
to properly apply per-app locales and trigger configuration changes.

- Change MainActivity and WidgetConfigActivity to extend AppCompatActivity.
- Apply the saved locale in WidgetConfigActivity.onCreate before super.onCreate().
- Switch the app theme parent to Theme.AppCompat.DayNight.NoActionBar so
  AppCompatActivity is happy while Compose theming remains unchanged.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: nichu42

app/src/main/java/de/nichu42/boxviewer/MainActivity.kt

@@ -6,10 +6,10 @@ import android.os.Bundle
 import android.widget.Toast
 import androidx.core.content.edit
 import androidx.core.net.toUri
-import androidx.activity.ComponentActivity
 import androidx.activity.compose.setContent
 import androidx.activity.enableEdgeToEdge
 import androidx.activity.viewModels
+import androidx.appcompat.app.AppCompatActivity
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.core.splashscreen.SplashScreen.Companion.installSplashScreen
 import androidx.compose.foundation.layout.padding
@@ -51,7 +51,7 @@ import androidx.compose.ui.res.stringResource
 import de.nichu42.boxviewer.R
 import kotlinx.coroutines.flow.MutableStateFlow
 
-class MainActivity : ComponentActivity() {
+class MainActivity : AppCompatActivity() {
 
     private val pendingBoxIdFromWidget = MutableStateFlow<String?>(null)
     private val pendingAddBoxId = MutableStateFlow<String?>(null)

app/src/main/java/de/nichu42/boxviewer/ui/WidgetConfigActivity.kt

@@ -3,23 +3,25 @@ package de.nichu42.boxviewer.ui
 import android.appwidget.AppWidgetManager
 import android.content.Intent
 import android.os.Bundle
-import androidx.activity.ComponentActivity
 import androidx.activity.compose.setContent
 import androidx.activity.enableEdgeToEdge
+import androidx.appcompat.app.AppCompatActivity
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Surface
 import androidx.compose.ui.Modifier
 import de.nichu42.boxviewer.data.db.SenseBoxDatabase
 import de.nichu42.boxviewer.data.repository.SenseBoxRepository
+import de.nichu42.boxviewer.util.LocaleHelper
 
 import de.nichu42.boxviewer.ui.theme.MyApplicationTheme
 
-class WidgetConfigActivity : ComponentActivity() {
+class WidgetConfigActivity : AppCompatActivity() {
 
     private var appWidgetId = AppWidgetManager.INVALID_APPWIDGET_ID
 
     override fun onCreate(savedInstanceState: Bundle?) {
+        LocaleHelper.applySavedLocale(this)
         super.onCreate(savedInstanceState)
         enableEdgeToEdge()
 

app/src/main/res/values/themes.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
 
-    <style name="Theme.MyApplication" parent="android:Theme.DeviceDefault.NoActionBar">
+    <style name="Theme.MyApplication" parent="Theme.AppCompat.DayNight.NoActionBar">
         <item name="android:windowBackground">@color/splash_background</item>
     </style>