fix(player): re-arm the cursor idle timer when playback changes

The idle countdown that hides the cursor and the play/pause overlay was only
started from mousemove. A cursor that stayed still over the player while a
click, a key or a scrub release started playback never got a countdown, so
the overlay stayed on the video until the mouse moved again.

Arm the timer from one place and rerun it whenever playback or fullscreen
changes, keeping the cursor-over-player state in a ref so the same rule
applies from every entry point.

components/video-page-content.tsx

@@ -214,7 +214,6 @@ export function VideoPageContent({
     setActiveVersionId,
   });
 
-  // Cursor idle detection: hide overlay when cursor idle for 3s while playing
   // Memoize version selection handler to prevent recreating on each render
   const handleVersionSelect = useCallback(
     (versionId: string) => {