refactor(player): share the cursor idle hook and stop waking on element pauses

Move the cursor idle logic into useCursorIdle and use it from both the video
page and the compare page, which carried its own copy. Only pointer activity
wakes the cursor now: a pause/play pair the element emits on its own (a
rebuffer, a source switch) leaves the idle state alone instead of bringing
the chrome back for a second. The fullscreen-while-paused arming is gone,
nothing rendered it. The scrub test now leaves the player before pressing
the timeline, as the real layout forces.

tests/component/hooks/use-video-player.test.ts

@@ -433,20 +433,25 @@ describe('useVideoPlayer cursor idling', () => {
     expect(result.current.cursorIdle).toBe(true);
   });
 
-  it('goes idle again after a scrub resumes playback without the cursor moving', () => {
+  it('stays awake through a scrub and idles again once the cursor returns', () => {
     const { result, video } = renderPlayer();
     act(() => result.current.handleVideoMouseMove());
     startPlayback(video);
     act(() => vi.advanceTimersByTime(IDLE_DELAY_MS));
     expect(result.current.cursorIdle).toBe(true);
 
-    // The element reports the pause the scrub asked for, then the resume.
+    // The timeline sits outside the player, so reaching it leaves the player
+    // first; the element then reports the pause the scrub asked for and the
+    // resume on release.
+    act(() => result.current.handleVideoMouseLeave());
     act(() => result.current.handleTimelineMouseDown(mouseEventAt(50)));
     stopPlayback(video);
-    expect(result.current.cursorIdle).toBe(false);
     act(() => result.current.handleTimelineMouseUp());
     startPlayback(video);
+    act(() => vi.advanceTimersByTime(IDLE_DELAY_MS * 5));
+    expect(result.current.cursorIdle).toBe(false);
 
+    act(() => result.current.handleVideoMouseMove());
     act(() => vi.advanceTimersByTime(IDLE_DELAY_MS));
     expect(result.current.cursorIdle).toBe(true);
   });
@@ -466,7 +471,7 @@ describe('useVideoPlayer cursor idling', () => {
     expect(result.current.cursorIdle).toBe(true);
   });
 
-  it('never idles while paused outside fullscreen', () => {
+  it('never idles while paused', () => {
     const { result } = renderPlayer();
     act(() => result.current.handleVideoMouseMove());
 
@@ -484,15 +489,18 @@ describe('useVideoPlayer cursor idling', () => {
     expect(result.current.cursorIdle).toBe(false);
   });
 
-  it('wakes as soon as playback pauses', () => {
+  it('stays idle across a pause and play the element emits on its own', () => {
     const { result, video } = renderPlayer();
     act(() => result.current.handleVideoMouseMove());
     startPlayback(video);
     act(() => vi.advanceTimersByTime(IDLE_DELAY_MS));
     expect(result.current.cursorIdle).toBe(true);
 
+    // A rebuffer or a source switch pauses and resumes without any pointer
+    // activity, so the cursor must not come back for a second on every stall.
     stopPlayback(video);
-    expect(result.current.cursorIdle).toBe(false);
+    startPlayback(video);
+    expect(result.current.cursorIdle).toBe(true);
   });
 });