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/components/PlayerModal.tsx

@@ -23,6 +23,7 @@ import {
 } from "lucide-react";
 import Avatar from "./Avatar";
 import AddToPlaylist from "./AddToPlaylist";
+import { modalCount } from "./Modal";
 import DownloadButton from "./DownloadButton";
 import { api, type Video } from "../lib/api";
 import {
@@ -375,6 +376,9 @@ export default function PlayerModal({
       if (e.key === "Escape") {
         // In fullscreen, let the browser's Esc exit fullscreen only — don't also close the modal.
         if (document.fullscreenElement) return;
+        // Defer to any Modal opened above the player (e.g. the download dialog): its Escape closes
+        // it, ours would otherwise also fire and close the player underneath it (U-C).
+        if (modalCount() > 0) return;
         onClose();
         return;
       }