test(playback): let the overlay's signal write schedule its own render

Review follow-up (Greptile): the test forced a render with
fixture.detectChanges() after the debounce timer, so it would pass even
if the signal write stopped scheduling an OnPush render. It now runs the
fixture with autoDetectChanges and only advances the fake timers; with
plain fields under OnPush the overlay never renders and the test fails.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/playlist/m3u/feature-player/src/lib/video-player/video-player.component.fullscreen-panel.spec.ts

@@ -252,20 +252,22 @@ describe('VideoPlayerComponent fullscreen channel panel + zapping', () => {
     });
 
     // OnPush: the overlay hides from a 2 s timer, outside any template
-    // event, so it must leave the DOM without a zone-triggered tick.
-    it('hides the channel-number overlay when its debounce fires', () => {
+    // event, so the signal write itself must schedule the render. The test
+    // never forces one after the timer: a plain-field write would leave the
+    // overlay in the DOM.
+    it('hides the channel-number overlay when its debounce fires', async () => {
         jest.useFakeTimers();
         try {
             const overlay = () =>
                 (fixture.nativeElement as HTMLElement).querySelector(
                     '.channel-number-overlay'
                 );
+            fixture.autoDetectChanges();
             component.handleChannelNumberInput('2');
-            fixture.detectChanges();
+            await jest.advanceTimersByTimeAsync(50);
             expect(overlay()?.textContent).toBe('2');
 
-            jest.advanceTimersByTime(2000);
-            fixture.detectChanges();
+            await jest.advanceTimersByTimeAsync(2000);
 
             expect(overlay()).toBeNull();
             expect(storeMock.dispatch).toHaveBeenCalledWith(