build: upgrade to Flutter 3.47.4 (AGP 9.1 / Gradle 9.3, iOS 15 + UIScene), refresh deps and CI

Flutter 3.24.5 -> 3.47.4 with the matching toolchain changes:

- pubspec: Dart ^3.11, Firebase core 4 / auth 6 / firestore 6 / storage 13,
  drop unused image_cropper, logging, change_app_package_name,
  pdf_widget_wrapper; pin path_provider_android <2.3 (needs NDK/CMake, not
  feasible on the ARM64 Gitea runner)
- Dart: CardTheme -> CardThemeData, replace deprecated withOpacity,
  Matrix4.scale, DropdownButtonFormField.value
- iOS: deployment target 15.0, UIScene lifecycle (AppDelegate/Info.plist),
  untrack stale Podfile.lock, add LaunchImage asset set
- Android: Gradle 9.3.1, AGP 9.1.0, Kotlin 2.4.0, google-services 4.5.0,
  layout.buildDirectory instead of removed Project.buildDir, remove manifest
  package attribute and duplicate MainActivity, kotlin.incremental=false
- CI: pin FLUTTER_VERSION in both workflows; iOS on macos-26 with SwiftPM
  disabled (CocoaPods only); Gitea job keeps cirruslabs 3.44.0 as base image
  (images discontinued) and switches the bundled Flutter SDK by git tag

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

android/app/build.gradle

@@ -1,60 +1,34 @@
 plugins {
     id "com.android.application"
-    id "kotlin-android"
+    // The Flutter Gradle Plugin must be applied after the Android and Kotlin Gradle plugins.
+    // (With android.builtInKotlin=false the Flutter plugin applies kotlin-android itself.)
     id "dev.flutter.flutter-gradle-plugin"
     id "com.google.gms.google-services"
 }
 
-def localProperties = new Properties()
-def localPropertiesFile = rootProject.file('local.properties')
-if (localPropertiesFile.exists()) {
-    localPropertiesFile.withReader('UTF-8') { reader ->
-        localProperties.load(reader)
-    }
-}
-
-def flutterVersionCode = localProperties.getProperty('flutter.versionCode')
-if (flutterVersionCode == null) {
-    flutterVersionCode = '1'
-}
-
-def flutterVersionName = localProperties.getProperty('flutter.versionName')
-if (flutterVersionName == null) {
-    flutterVersionName = '1.0'
-}
-
 android {
     namespace "com.oggauergemeindetrommler.app"
-    compileSdkVersion flutter.compileSdkVersion
-    ndkVersion "26.1.10909125"
+    compileSdk flutter.compileSdkVersion
+    ndkVersion flutter.ndkVersion
 
     compileOptions {
         sourceCompatibility JavaVersion.VERSION_17
         targetCompatibility JavaVersion.VERSION_17
     }
 
-    kotlinOptions {
-        jvmTarget = '17'
-    }
-
     buildFeatures {
         buildConfig = true
     }
 
-    sourceSets {
-        main.java.srcDirs += 'src/main/kotlin'
-    }
-
     defaultConfig {
-        // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
         applicationId "com.oggauergemeindetrommler.app"
-        // You can update the following values to match your application needs.
-        // For more information, see: https://docs.flutter.dev/deployment/android#reviewing-the-build-configuration.
-        minSdkVersion 23
-        targetSdkVersion flutter.targetSdkVersion
-        versionCode flutterVersionCode.toInteger()
-        versionName flutterVersionName
-        multiDexEnabled true
+        // Flutter 3.47 defaults to 24; 23 (Android 6.0) is still supported and
+        // is also the minimum required by the current Firebase Android SDKs.
+        minSdkVersion flutter.minSdkVersion
+        targetSdk flutter.targetSdkVersion
+        // Read from pubspec.yaml (via local.properties); defaults to 1 / "1.0".
+        versionCode flutter.versionCode
+        versionName flutter.versionName
     }
 
     buildTypes {
@@ -66,8 +40,12 @@ android {
     }
 }
 
+kotlin {
+    compilerOptions {
+        jvmTarget = org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17
+    }
+}
+
 flutter {
     source '../..'
 }
-
-dependencies {}