feat(design): the download, notification and Scheduler action lists (C1) — the rows' "…", the band's and the strip's "…" (E28 S3e3)

A download row keeps play (pause / resume / retry in the queue) and the save link; the editors,
sharing, re-download, the copies and cancel / delete / remove moved into its "…"
(useDownloadActions). A link inside the row keeps the browser's own right-click menu. A
notification row keeps its link and its unread mark and shows its dismiss on hover; an activity
notice's Find in feed and Undo are in its "…". The inbox band keeps Mark all read and puts Clear
everything, now behind a confirm, in its "…". The Scheduler strip keeps Run all and Pause and puts
Purge discovery in its "…". Polled lists key their menus by id (keyOf). ui/menuGroups draws a
rule only between two non-empty groups. Find in feed also drops the tag, search and age filters
that could hide the video it looks for.

frontend/src/components/DownloadCenter.confirm.dom.test.tsx

@@ -77,6 +77,24 @@ afterEach(() => {
   mocks.confirm.mockClear();
 });
 
+/** Pick `label` from the row's menu, opened by its "…". The surface is visibility:hidden in jsdom
+ *  (floating-ui never positions it), so the row is matched on its text. */
+async function pick(row: string, label: string) {
+  const more = screen
+    .getByText(row)
+    .closest<HTMLElement>("[data-nav-index]")!
+    .querySelector<HTMLElement>('button[aria-label="downloads.rowMenu"]')!;
+  fireEvent.click(more);
+  const item = await waitFor(() => {
+    const found = screen
+      .getAllByRole("menuitem", { hidden: true })
+      .find((b) => b.textContent === label);
+    expect(found).toBeTruthy();
+    return found!;
+  });
+  fireEvent.click(item);
+}
+
 describe("DownloadCenter confirm dialogs", () => {
   it("label the confirm button with the action, not the dialog's question", async () => {
     mocks.jobs = [job(1, "running"), job(2, "done")];
@@ -86,12 +104,15 @@ describe("DownloadCenter confirm dialogs", () => {
       </QueryClientProvider>,
     );
 
-    fireEvent.click(screen.getByTitle("downloads.actions.cancel"));
+    // E28 C1: the destructive and rare row buttons live in the row's "…".
+    await pick("Clip 1", "downloads.actions.cancel");
     await waitFor(() => expect(mocks.confirm).toHaveBeenCalledTimes(1));
     // The tab's label shares its button with a count badge.
     fireEvent.click(screen.getByRole("button", { name: /downloads\.tabs\.done/ }));
-    fireEvent.click(await screen.findByTitle("downloads.actions.redownload"));
-    fireEvent.click(screen.getByTitle("downloads.actions.delete"));
+    await screen.findByText("Clip 2");
+    await pick("Clip 2", "downloads.actions.redownload");
+    await waitFor(() => expect(mocks.confirm).toHaveBeenCalledTimes(2));
+    await pick("Clip 2", "downloads.actions.delete");
     await waitFor(() => expect(mocks.confirm).toHaveBeenCalledTimes(3));
 
     expect(mocks.confirm.mock.calls.map(([o]) => [o.title, o.confirmLabel])).toEqual([