fix(player): Escape coordination, focused-Space, light-theme menus (U-C, U-3.1.4, U-3.3.12)

Three player/overlay interaction fixes (PlexPlayer changes share a file, hence one
commit):
- U-C (Escape double-close): useDismiss's Escape now stopPropagation()s (its document
  listener bubbles before a player's window listener, so one Escape closes only the
  popover, not the popover AND the player). Modal exports modalCount(); both players'
  Escape defers when a Modal is open above them, so Escape closes the dialog, not the
  player under it and then the dialog.
- U-3.1.4: PlexPlayer's Space now defers to a focused BUTTON/A (e.g. "Skip intro")
  instead of toggling playback — matching PlayerModal.
- U-3.3.12: the audio/subtitle menus used theme-adaptive glass-menu + forced
  text-white (white-on-white in light theme); they now use the player's own explicit
  dark panel (border-white/15 + bg-neutral-900/95), readable in both themes.

frontend/src/lib/useDismiss.ts

@@ -17,7 +17,13 @@ export function useDismiss(
       if (!list.some((r) => r.current?.contains(target))) onClose();
     };
     const onKey = (e: KeyboardEvent) => {
-      if (e.key === "Escape") onClose();
+      if (e.key === "Escape") {
+        // 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.)
+        e.stopPropagation();
+        onClose();
+      }
     };
     document.addEventListener("mousedown", onDown);
     document.addEventListener("keydown", onKey);