feat(design): a channel's and a Plex playlist's one action list (C1) — the row's "…", Delete + undo, an action toast's 8 s floor (E28 S3e2)

- Channels: the row's full-history, hide and unsubscribe buttons become its "…" at the row end
  (useChannelActions: open, pin, YouTube, copy name / link, full history or the admin reset,
  hide with an undo toast, unsubscribe behind its danger confirm); the card layout docks the "…"
  beside the name (ChannelLayoutGrid moreKey). The admin reset's confirm now names the reset.
- Plex playlist page: a title, a show group and a season each open the page's one row menu (a
  title's is its usePlexCardActions list plus the removal); no X at rest; removals take an undo
  toast whose Undo puts every row back at its own index in one request (bulk add `positions`);
  j/k walk the visible rows, Delete removes the walked one; rename and delete in the header's "…".
- notify: a toast with an action lives at least 8 s (the owner's call), whatever the toast setting.

frontend/src/components/PlexPlaylistView.header.dom.test.tsx

@@ -5,7 +5,7 @@
 // (E9 review). The runtime sums the WHOLE list, an unknown duration counts as nothing, and a list
 // nothing sums for says no runtime at all.
 import { describe, it, expect, vi, beforeAll, afterEach } from "vitest";
-import { render, cleanup, screen, fireEvent } from "@testing-library/react";
+import { render, cleanup, screen, fireEvent, waitFor } from "@testing-library/react";
 import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
 
 vi.mock("react-i18next", async (importOriginal) => ({
@@ -60,6 +60,20 @@ async function meta(items: PlexCard[]) {
   ).textContent;
 }
 
+/** Pick `label` from the menu `open` opens. The surface is visibility:hidden in jsdom (floating-ui
+ *  never positions it), so the row is matched on its text. */
+async function pickFromMenu(open: () => void, label: string) {
+  open();
+  const row = await waitFor(() => {
+    const found = screen
+      .getAllByRole("menuitem", { hidden: true })
+      .find((b) => b.textContent === label);
+    expect(found).toBeTruthy();
+    return found!;
+  });
+  fireEvent.click(row);
+}
+
 describe("PlexPlaylistView · the header's meta line", () => {
   it("sums the known runtimes and counts an unknown one as nothing", async () => {
     expect(await meta([movie("1", 5400), movie("2"), movie("3", 1800)])).toBe(
@@ -80,8 +94,11 @@ describe("PlexPlaylistView · rename", () => {
     const write = vi.spyOn(api, "plexRenamePlaylist").mockResolvedValue({} as never);
     await meta([movie("1", 5400)]);
     for (const value of [null, "   "]) {
-      fireEvent.click(screen.getByRole("button", { name: "plex.playlist.rename" }));
-      const field = screen.getByRole("textbox", { name: "plex.playlist.rename" });
+      await pickFromMenu(
+        () => fireEvent.click(screen.getByRole("button", { name: "plex.playlist.menu" })),
+        "plex.playlist.rename",
+      );
+      const field = await screen.findByRole("textbox", { name: "plex.playlist.rename" });
       if (value !== null) fireEvent.change(field, { target: { value } });
       fireEvent.keyDown(field, { key: "Enter" });
       await screen.findByRole("heading", { name: "Films" });