feat: Add audio file upload and transcription support

- Add AudioUploadSection component with drag-and-drop support
- Implement audio converter using symphonia for M4A/MP3/FLAC support
- Add transcribe_audio_file command for direct file transcription
- Add comprehensive tests for upload component and converter
- Update UI to show 'Upload' section in sidebar
- Support multiple audio formats beyond just WAV

Test coverage:
- Frontend: 43 tests for AudioUploadSection
- Backend: 9 tests for converter and file operations

Author: moinulmoin

src-tauri/Cargo.lock

@@ -28,6 +28,7 @@ serde_json = "1"
 whisper-rs = { version = "0.14.3" }
 cpal = "0.16.0"
 hound = "3.5.1"
+symphonia = { version = "0.5", features = ["all"] }
 rubato = "0.15"
 futures-util = "0.3.31"
 tokio = { version = "1.46.0", features = ["full"] }