feat: download option for speaker diarization

Issue Description

Currently, users can listen to the speaker diarization output within the application, but there is no option to download the processed audio file for offline access or sharing.

A download functionality needs to be added to the speaker diarization section so users can easily save the generated audio file directly from the UI.

Requirements

• Add a download button in the speaker diarization output section
• Allow users to download the generated diarized audio file
• Ensure the button appears only when audio output is available
• Maintain existing application logic and UI behavior
• Keep the implementation lightweight and responsive

Expected Outcome

Users should be able to click the download button and save the diarized audio file locally without affecting existing playback or diarization functionality.