fix(ui): a removed chip's focus outlives its neighbour; a scroll restore yields to the reader

A chip handed its focus to a Clear all or +N that went in the same removal, and the focus fell to
the body. The restore now stops when the reader scrolls, and finishes the way once the Back-to-top
spacer brings the saved spot within reach.

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

@@ -3,7 +3,7 @@
 // E28 S3b: the chip family (docs/DESIGN.md "One primitive per button family"). One geometry for a
 // filter, an applied narrowing, a tag and a suggestion, where five files had five.
 import { afterEach, describe, expect, it, vi } from "vitest";
-import { act, cleanup, fireEvent, render, screen } from "@testing-library/react";
+import { act, cleanup, fireEvent, render, screen, waitFor } from "@testing-library/react";
 import { useState } from "react";
 import { Chip, DismissibleChip } from "./Chip";
 import { chipClass } from "./chipStyles";
@@ -70,6 +70,37 @@ describe("Chip", () => {
     expect(document.activeElement).toBe(screen.getByRole("button", { name: "Remove News" }));
   });
 
+  // Round 3: the neighbour it hands the focus to can go in the same removal — the "Clear all" that
+  // only shows beside two filters. The focus then goes to the chip before, not to <body>.
+  it("a removing chip whose neighbour goes with it hands the focus to the chip before", async () => {
+    function Row() {
+      const [chips, setChips] = useState(["Music", "News"]);
+      return (
+        <div>
+          {chips.map((c) => (
+            <Chip
+              key={c}
+              variant="token"
+              removeLabel={`Remove ${c}`}
+              onClick={() => setChips((all) => all.filter((x) => x !== c))}
+            >
+              {c}
+            </Chip>
+          ))}
+          {chips.length > 1 && <button onClick={() => setChips([])}>Clear all</button>}
+        </div>
+      );
+    }
+    render(<Row />);
+    const news = screen.getByRole("button", { name: "Remove News" });
+    act(() => news.focus());
+    fireEvent.click(news, { detail: 0 });
+    expect(screen.queryByRole("button", { name: "Clear all" })).toBeNull();
+    await waitFor(() =>
+      expect(document.activeElement).toBe(screen.getByRole("button", { name: "Remove Music" })),
+    );
+  });
+
   it("the measuring mirror lays out exactly like the chip it measures", () => {
     render(
       <Chip variant="tag" size="xs">