fix(audio): remove MediaRecorder timeslice to prevent truncated recordings on mobile

Mobile browsers (especially iOS Safari) drop or overwrite audio chunks when using recorder.start(500), resulting in recordings that are only 2-10 seconds despite recording for much longer. Removing the timeslice parameter lets the MediaRecorder buffer all data internally until stop() is called, ensuring complete recordings on mobile devices.

Co-authored-by: Qwen-Coder [email protected]