test(qa): open the phone tab sheets in phone-width harness checks

At 720px and narrower the panels live in the phone shell's tab sheets, so the
camera, scene and map-source tray harnesses open the matching tab (from the
keyboard where they check focus rings) before measuring, wait for the shell to
follow a viewport change, measure the container that actually scrolls, and run
the pin and compact-wing checks at 800px where the narrow desktop dock still
exists.

scripts/qa-scene-controls.mjs

@@ -329,6 +329,9 @@ try {
   await page.keyboard.press('Escape');
   await page.screenshot({ path: path.join(shots, 'desktop.png') });
   await page.setViewport({ width: 390, height: 844 });
+  // Phones present Scenes in the Layers tab's sheet.
+  await page.click('#mobile-tab-bar [data-mobile-sheet="layers"]');
+  await new Promise((resolve) => setTimeout(resolve, 400));
   await page.screenshot({ path: path.join(shots, 'narrow.png') });
   check(
     'Scene controls stay inside the narrow viewport',