Add output formats and quality controls

[phoenixray2000]

Summary

• Add WAV, FLAC, and MP3 output profiles with Balanced and High Quality presets.
• Add Keep Stereo and live Preview controls to the Settings window.
• Encode WAV/FLAC through soundfile and MP3 through lameenc with profile-specific bitrates.
• Document the new output profile options in README.

Validation

• ..venv\Scripts\python.exe -m unittest discover -s tests -v (14 tests OK)
• ..venv\Scripts\python.exe -m py_compile audio_recorder.py gui.py main.py
• Previously built QuickAudioRecorder.exe with PyInstaller and copied it to D:\Program Files\QuickAudioRecorder.