fix(toast,overlay): review round 1 — close toast-timer edge, document Escape limit

Review found two low-severity items:
- toast: armDismiss now always clears the prior timer (and arms only when duration is
  truthy), so a coalesced repeat that upgrades a toast to requiresInteraction no longer
  lets the original timer fire and dismiss it. Was a pre-existing gap the C-3.25 change
  hadn't closed.
- overlay: documented the known limitation of useDismiss's blanket stopPropagation — a
  PlexPlayer menu open during an auto-skip countdown swallows the Escape that would also
  cancel the skip. Proper fix needs R8's shared layer-registry (topmost-only dispatch),
  not a broad stopPropagation; accepted until then.

frontend/src/lib/useDismiss.ts

@@ -21,6 +21,12 @@ export function useDismiss(
         // Stop the same Escape from also reaching a player's window-level listener underneath —
         // this document listener bubbles first, so one Escape closes only this popover, not the
         // popover AND the player behind it. (U-C quick-fix.)
+        //
+        // KNOWN LIMITATION (accepted, → R8 popover-platform): because this is a blanket
+        // stopPropagation, a PlexPlayer settings/tracks menu open DURING an auto-skip countdown
+        // swallows the Escape that would otherwise ALSO cancel the skip — Escape closes the menu,
+        // and the skip proceeds. Properly fixing this needs the shared layer-registry R8 builds
+        // (topmost-only dispatch), not a broad stopPropagation.
         e.stopPropagation();
         onClose();
       }