A slim horizontal master-volume slider in its own slot between the
visualizer and the timeline (TASKS.md). Perceptual->linear gain so it
ramps like iTunes; persists to preferences.json (debounced so it doesn't
thrash the theme). Clicking jumps to the spot via a new ClickJumpSlider
base extracted from SeekSlider.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
