fix(ui): toasts raised while a full-screen player is open show inside it, not under its scrim

The app's Toaster lives in the content column, which is a stacking context (its `@container` implies
layout containment), so both full-screen players — portalled to <body> at the same z-index — painted
over every toast. Round 1's "a failed Remove is reported" fix was therefore still silent inside the
player: its toast sat under an 80% black, blurred scrim (elementFromPoint returned the scrim), and a
click on it closed the player.

An overlay now mounts its own `<Toaster overlay />`, and exactly one host shows the toasts: the most
recently mounted overlay, else the app's. Same component, same look — and inside the aria-modal
dialog, where a screen reader can still reach it. A click on a toast inside an overlay stays there.
Both players get one (the Plex player's also works in native fullscreen, where nothing outside the
fullscreen element is drawn). Verified on localdev: the removal failure reads above the scrim,
bottom-left, and clicking it leaves the player open.

frontend/src/components/ui/Toaster.dom.test.tsx

@@ -0,0 +1,61 @@
+// @vitest-environment jsdom
+//
+// Which Toaster shows the toasts. The app's own sits in the content column, which is a stacking
+// context — so a full-screen player portalled to <body> at the same z painted over every toast: a
+// failed Remove raised while watching was drawn under the player's scrim, and clicking it closed
+// the player. An overlay mounts its own host, and exactly one host shows the toasts.
+import { describe, it, expect, vi, afterEach } from "vitest";
+import { render, screen, fireEvent, cleanup, act } from "@testing-library/react";
+
+vi.mock("react-i18next", async (importOriginal) => {
+  const actual = await importOriginal<typeof import("react-i18next")>();
+  return { ...actual, useTranslation: () => ({ t: (key: string) => key }) };
+});
+
+import Toaster from "./Toaster";
+import { clearAll, notify } from "../../lib/notifications";
+
+afterEach(() => {
+  cleanup();
+  act(() => clearAll());
+});
+
+const hosts = () => Array.from(document.querySelectorAll("[aria-live='polite']"));
+
+describe("Toaster — one host shows the toasts", () => {
+  it("moves the toasts into an open overlay, and back when it closes", () => {
+    const app = render(
+      <div data-testid="app">
+        <Toaster />
+      </div>,
+    );
+    act(() => void notify({ level: "error", message: "Couldn't remove the video." }));
+    expect(screen.getByTestId("app").textContent).toContain("Couldn't remove the video.");
+
+    const overlay = render(
+      <div data-testid="overlay">
+        <Toaster overlay />
+      </div>,
+    );
+    expect(screen.getByTestId("overlay").textContent).toContain("Couldn't remove the video.");
+    expect(screen.getByTestId("app").textContent).not.toContain("Couldn't remove the video.");
+    // Both live regions stay mounted — a polite region has to pre-exist to be announced.
+    expect(hosts()).toHaveLength(2);
+
+    overlay.unmount();
+    expect(screen.getByTestId("app").textContent).toContain("Couldn't remove the video.");
+    app.unmount();
+  });
+
+  it("does not let a click on a toast reach the overlay's backdrop", () => {
+    const backdrop = vi.fn();
+    render(
+      <div onClick={backdrop}>
+        <Toaster overlay />
+      </div>,
+    );
+    act(() => void notify({ level: "error", message: "boom" }));
+    fireEvent.click(screen.getByText("boom"));
+    expect(backdrop).not.toHaveBeenCalled();
+  });
+});

frontend/src/components/ui/Toaster.tsx

@@ -1,4 +1,4 @@
-import { useSyncExternalStore } from "react";
+import { useEffect, useId, useSyncExternalStore } from "react";
 import { useTranslation } from "react-i18next";
 import { AlertCircle, AlertTriangle, CheckCircle2, Info, X, XCircle } from "lucide-react";
 import { dismiss, getActiveToasts, subscribe, type NotifLevel } from "../../lib/notifications";
@@ -11,9 +11,36 @@ export const LEVEL_STYLE: Record<NotifLevel, { icon: typeof Info; color: string;
   fatal: { icon: XCircle, color: "text-danger", bar: "bg-danger" },
 };
 
-export default function Toaster() {
+// Overlay hosts. The app's own Toaster sits in the content column, and that column is a stacking
+// context (its `@container` implies layout containment) — so a full-screen player, portalled to
+// <body> at the same z-overlay, painted over every toast: a failure raised while watching was
+// drawn under an 80% black, blurred scrim, and a click on it closed the player. Such an overlay
+// mounts its OWN `<Toaster overlay />` inside itself instead, and exactly one host shows the
+// toasts: the most recently mounted overlay, else the app's. Same component, same look — and inside
+// the overlay's aria-modal dialog, where a screen reader can still reach it.
+let overlayHosts: string[] = [];
+const hostListeners = new Set<() => void>();
+const subscribeHosts = (l: () => void) => {
+  hostListeners.add(l);
+  return () => void hostListeners.delete(l);
+};
+const topHost = () => overlayHosts[overlayHosts.length - 1] ?? null;
+const setHosts = (next: string[]) => {
+  overlayHosts = next;
+  hostListeners.forEach((l) => l());
+};
+
+export default function Toaster({ overlay = false }: { overlay?: boolean }) {
   const { t } = useTranslation();
-  const toasts = useSyncExternalStore(subscribe, getActiveToasts, getActiveToasts);
+  const id = useId();
+  useEffect(() => {
+    if (!overlay) return;
+    setHosts([...overlayHosts, id]);
+    return () => setHosts(overlayHosts.filter((h) => h !== id));
+  }, [overlay, id]);
+  const top = useSyncExternalStore(subscribeHosts, topHost, topHost);
+  const active = useSyncExternalStore(subscribe, getActiveToasts, getActiveToasts);
+  const toasts = top === (overlay ? id : null) ? active : [];
 
   return (
     // Stable, always-mounted polite live region — a polite region must PRE-EXIST in the DOM for a
@@ -25,6 +52,8 @@ export default function Toaster() {
     <div
       aria-live="polite"
       className="absolute bottom-4 left-4 z-overlay flex flex-col gap-2 w-80 max-w-[calc(100vw-2rem)]"
+      // Inside an overlay, a click on a toast is not a click on the overlay's backdrop.
+      onClick={overlay ? (e) => e.stopPropagation() : undefined}
     >
       {toasts.map((toast) => {
         const { icon: Icon, color, bar } = LEVEL_STYLE[toast.level];