fix(ui): a toast host ranks by when its overlay opened, and an overlay keeps its Escape, its dialog and its navigation straight

Deep-review round 4, the overlays.

- Toast hosts were ranked by mount time, and PlayerModal swaps its host on every fullscreen change:
  leaving true fullscreen with the download dialog open put the player's host back on top, so toasts
  were drawn under that dialog's scrim and a click on one closed the dialog. Each overlay takes a
  rank once, when it opens (`useOverlayOrder`), and hands it to every host it renders.
- A dialog open while fullscreen is left keeps a stable portal container (moved, not re-created):
  React tore the portal down when `fsRoot` changed, resetting a half-filled form and dropping focus
  to <body>. Focus is put back after the move.
- The onboarding wizard is a layer, not a raw document listener: one Escape used to dismiss the
  error dialog over it AND end onboarding, skipping the write-scope step.
- `navigateTo` (a toast's "View", clicked inside the player's own host) goes over the overlays it
  unmounts, so the player's Back-to-close cleanup no longer pops the page it just opened — the same
  fix Shift+W already had. The access-requests toast action too.
- The live region arms itself a task after it takes over inherited toasts: React flushes effects in
  the same task as that render, so the "silent inheritance" arming was a no-op.
- The overlay-host guard matches class tokens in any order (PlexPlayer's root was never checked),
  globs `ui/` too (ui/Modal was not checked either), and requires the rank.

frontend/src/components/PlexPlayer.tsx

@@ -43,7 +43,7 @@ import { PlexPlayerSettings } from "./PlexPlayerSettings";
 import { PlexStatsOverlay } from "./PlexStatsOverlay";
 import { createFragMeter } from "../lib/plexStats";
 import { UpNextCard } from "./UpNextCard";
-import Toaster from "./ui/Toaster";
+import Toaster, { useOverlayOrder } from "./ui/Toaster";
 import {
   playhead,
   useAutoSkip,
@@ -793,6 +793,8 @@ export default function PlexPlayer({ itemId, onClose, queue }: Props) {
   useKeyScope("plexPlayer");
   useHelpConditions({ episode: detail?.kind === "episode" });
 
+  // Its toast host's rank among open overlays (see ui/Toaster).
+  const overlayOrder = useOverlayOrder();
   // This player is a dismissable layer: register it so a Modal or popover opened ABOVE it (its own
   // settings/tracks menus included) takes Escape first and this player defers (R8 S3).
   const layerIdRef = useRef<number | null>(null);
@@ -1515,7 +1517,7 @@ export default function PlexPlayer({ itemId, onClose, queue }: Props) {
       )}
       {/* The app's Toaster is underneath this full-screen player (and outside it in native
           fullscreen), so toasts raised while watching show here instead. See ui/Toaster. */}
-      <Toaster overlay />
+      <Toaster overlay order={overlayOrder} />
     </div>,
     document.body,
   );