The glass controls capsule can now be dragged anywhere over the video.
Position is stored as a fraction of the container size so it survives
window resizes and aspect-ratio driven sheet resizes, persists across
sessions via SettingsManager, and snaps back magnetically when dropped
near the default bottom-center spot. Travel is clamped so the capsule
stays inside the player and never overlaps the top button row. A
mouseDownCanMoveWindow=false backing view keeps the window's
movable-by-background behavior from swallowing the drag.
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