fix: preserve existing M4A metadata during embed and enable BuildConfig generation

android/app/build.gradle.kts

@@ -20,6 +20,10 @@ android {
     compileSdk = flutter.compileSdkVersion
     ndkVersion = flutter.ndkVersion
 
+    buildFeatures {
+        buildConfig = true
+    }
+
     compileOptions {
         isCoreLibraryDesugaringEnabled = true
         sourceCompatibility = JavaVersion.VERSION_17

lib/services/ffmpeg_service.dart

@@ -1473,7 +1473,7 @@ class FFmpegService {
     required String m4aPath,
     String? coverPath,
     Map<String, String>? metadata,
-    bool preserveMetadata = false,
+    bool preserveMetadata = true,
   }) async {
     final tempDir = await getTemporaryDirectory();
     final tempOutput = _nextTempEmbedPath(tempDir.path, '.m4a');