fix(plex): the player's ⋯ and tracks lists are real menus, and every close returns the focus

They were hand-built divs: no menu roles, no arrow keys, and Escape left the
focus on <body>. Both run on the popover engine now (media-tone rows), and the
tuning panel is a labelled dialog that takes the focus and hands it back to ⋯.

frontend/src/components/PlexPlayer.tabtrap.dom.test.tsx

@@ -8,7 +8,7 @@
 // the round-3 comment that handed the step prompt's trap to "the dialog below" assumed this one did
 // too. Its own file because `layerStack` is module state and these tests push into it.
 import { describe, it, expect, vi, beforeAll, afterEach } from "vitest";
-import { render, cleanup, waitFor, act } from "@testing-library/react";
+import { render, cleanup, waitFor, act, screen } from "@testing-library/react";
 import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
 
 vi.mock("react-i18next", async (importOriginal) => ({
@@ -116,6 +116,17 @@ const press = (key: string, shiftKey = false) =>
     );
   });
 
+// A menu's rows are named by their text: the surface is `visibility: hidden` until floating-ui has
+// measured it (never, under jsdom), and a hidden element's accessible name is empty.
+const menuItem = (label: string) =>
+  waitFor(() => {
+    const row = screen
+      .queryAllByRole("menuitem", { hidden: true })
+      .find((b) => b.textContent === label);
+    expect(row).toBeDefined();
+    return row!;
+  });
+
 describe("PlexPlayer · Tab stays inside the player", () => {
   it("pulls the focus back in when it is on the page behind", async () => {
     await mount();
@@ -160,9 +171,10 @@ describe("PlexPlayer · Tab stays inside the player", () => {
     const more = buttons().find((b) => b.getAttribute("aria-label") === "plex.player.more");
     expect(more).toBeDefined();
     act(() => more!.click());
-    const settings = buttons().find((b) => b.textContent === "plex.player.settings");
-    expect(settings).toBeDefined();
-    act(() => settings!.click());
+    // The ⋯ is a menu on the popover engine: it portals out of the player and traps for itself.
+    const settings = await menuItem("plex.player.settings");
+    act(() => settings.click());
+    await screen.findByRole("dialog", { name: "plex.player.settings" });
     const items = buttons();
     // The panel really opened — the trap now has to span its controls too.
     expect(items.length).toBeGreaterThan(before + 3);