feat: restore WAV as default output (aceradio compatibility)

acestep.cpp previously generated *.wav by default for maximum quality.
Later changed to mp3, but aceradio expects WAV input.

- Revert to WAV default to match aceradio workflow
- No conversion overhead or compatibility issues
- Preserves original high-quality generation logic

src/AceStepWorker.cpp

@@ -181,6 +181,7 @@ void AceStep::qwenProcFinished(int code, QProcess::ExitStatus status)
 	ditVaeArgs << "--text-encoder"<<request.textEncoderModelPath;
 	ditVaeArgs << "--dit"<<request.ditModelPath;
 	ditVaeArgs << "--vae"<<request.vaeModelPath;
+	ditVaeArgs << "--wav";
 
 	progressUpdate(60);