feat: replace custom FFmpeg AAR with ffmpeg_kit_flutter plugin, add Lossy format support (MP3/Opus)

- Replace custom ffmpeg-kit-with-lame.aar with ffmpeg_kit_flutter_new_audio plugin
- Rename MP3 option to Lossy with format selection (MP3 320kbps or Opus 128kbps)
- Add convertFlacToOpus() and convertFlacToLossy() functions in FFmpegService
- Update settings model: enableMp3Option -> enableLossyOption, add lossyFormat field
- Update download_queue_provider to use LOSSY quality with format from settings
- Remove FFMPEG_CHANNEL MethodChannel from MainActivity.kt
- Delete custom FFmpeg AAR files from android/app/libs/
- Add new localization strings for lossy format options

android/app/src/main/kotlin/com/zarz/spotiflac/MainActivity.kt

@@ -7,8 +7,6 @@ import io.flutter.embedding.engine.FlutterEngine
 import io.flutter.embedding.engine.FlutterShellArgs
 import io.flutter.plugin.common.MethodChannel
 import gobackend.Gobackend
-import com.arthenica.ffmpegkit.FFmpegKit
-import com.arthenica.ffmpegkit.ReturnCode
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.SupervisorJob
@@ -18,7 +16,6 @@ import java.util.Locale
 
 class MainActivity: FlutterActivity() {
     private val CHANNEL = "com.zarz.spotiflac/backend"
-    private val FFMPEG_CHANNEL = "com.zarz.spotiflac/ffmpeg"
     private val scope = CoroutineScope(SupervisorJob() + Dispatchers.Main)
 
     companion object {
@@ -901,37 +898,5 @@ class MainActivity: FlutterActivity() {
                 }
             }
         }
-        
-        // FFmpeg method channel
-        MethodChannel(flutterEngine.dartExecutor.binaryMessenger, FFMPEG_CHANNEL).setMethodCallHandler { call, result ->
-            scope.launch {
-                try {
-                    when (call.method) {
-                        "execute" -> {
-                            val command = call.argument<String>("command") ?: ""
-                            val session = withContext(Dispatchers.IO) {
-                                FFmpegKit.execute(command)
-                            }
-                            val returnCode = session.returnCode
-                            val output = session.output ?: ""
-                            result.success(mapOf(
-                                "success" to ReturnCode.isSuccess(returnCode),
-                                "returnCode" to (returnCode?.value ?: -1),
-                                "output" to output
-                            ))
-                        }
-                        "getVersion" -> {
-                            val session = withContext(Dispatchers.IO) {
-                                FFmpegKit.execute("-version")
-                            }
-                            result.success(session.output ?: "unknown")
-                        }
-                        else -> result.notImplemented()
-                    }
-                } catch (e: Exception) {
-                    result.error("FFMPEG_ERROR", e.message, null)
-                }
-            }
-        }
     }
 }