fix(plex): the player holds the page still and covers it whole; the row drops the countdown

On an iPad a drag on the video scrolled the page behind the player, and in Brave
dvh did not follow the toolbar, so a strip of the page showed under it. The
page is now locked without overscroll on a black root while the player is open,
and the player is sized from its fixed box. The time row keeps the position,
the length and the end clock; the countdown is gone (owner).

frontend/src/components/ui/dialogFocus.ts

@@ -62,7 +62,7 @@ export function trapTab(
 // second copy of the lock is gone.
 let scrollLocks = 0;
 let unlockedOverflow = "";
-function lockBodyScroll(): () => void {
+export function lockBodyScroll(): () => void {
   if (scrollLocks++ === 0) {
     unlockedOverflow = document.body.style.overflow;
     document.body.style.overflow = "hidden";