fix: pin mpv speed every playback tick so it can't drift to half

The x2/x4 toggle always derives the right speed (1/2/4), but mpv's speed could
still drift out of sync during the ab-loop playback (e.g. across loop seeks),
making it feel half-speed after x2 -> x4 -> x2. Reassert the desired speed on
each render tick while playing so mpv always matches the buttons.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

main.py

@@ -2890,6 +2890,13 @@ class MpvWidget(QWidget):
             tp = self._player.time_pos
             if tp is not None:
                 self.time_pos_changed.emit(tp)
+            # Pin mpv's speed to the desired value — it can otherwise drift out
+            # of sync (e.g. across ab-loop seeks) and feel like half-speed.
+            try:
+                if abs((self._player.speed or 1.0) - self._speed) > 1e-6:
+                    self._player.speed = self._speed
+            except Exception:
+                pass
             if self._wid_mode and self._overlay_widget and self._overlays:
                 self._overlay_widget.update()