Add clip duration spinner (2–30s, default 8s) replacing all hardcoded
8.0 references. Store clip_duration in DB for accurate re-export span
calculations. Add x2/x4 playback speed toggle buttons. On Windows, mpv
renders directly into the widget's native window handle (WId embedding)
instead of slow FBO readback; crop overlays use a transparent child
widget. Fix _poll_render crash when player is None after closeEvent.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Ethanfel
47f910644d