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

pubspec.lock

@@ -297,6 +297,22 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.1.4"
+  ffmpeg_kit_flutter_new_audio:
+    dependency: "direct main"
+    description:
+      name: ffmpeg_kit_flutter_new_audio
+      sha256: "0a698b46cd163c8e9917af75325c84d27871a2a8b2c37de3b40486cd0ab662ae"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.0.0"
+  ffmpeg_kit_flutter_platform_interface:
+    dependency: transitive
+    description:
+      name: ffmpeg_kit_flutter_platform_interface
+      sha256: addf046ae44e190ad0101b2fde2ad909a3cd08a2a109f6106d2f7048b7abedee
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.2.1"
   file:
     dependency: transitive
     description: