SIDpulse Tracker v0.2.22

Audio playback now runs in a separate process to protect it from UI stalls, with optimized PCM buffering and output conditioning.

Adds configurable underrun detection, subtle warning notifications, and Alt+F12 for audio settings.

Includes performance measurements and regression evidence:
https://github.com/FlyingFathead/sidpulse-tracker/blob/v0.2.22/docs/VALIDATION-v0.2.22.md