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.