The hide timer was gated on the pointer leaving the player view, which
never happens in fullscreen, so controls shown when pressing F stayed up
forever. Switch to idle-based hiding: mouse movement shows controls and
resets the 3s timer; controls fade after inactivity even while the
pointer rests over the video, unless it's on one of the control bars.
Entering fullscreen rebaselines hover tracking so the resize-driven
hover re-emission doesn't count as movement.
Also hide the mouse pointer (setHiddenUntilMouseMoves) when controls
hide in fullscreen, restoring it on exit or any mouse move.
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