fix(ui): the reader's own use of a stand-in stops the restore; the pill's name carries its cap

Round 2 of the deep review:
- A click on, or a key typed into, the focus keeper's stand-in fires no focusin, so a restore still
  polling for its list could take the focus from under the reader. A pointerdown or keydown now
  makes it the reader's own focus.
- The Jump-to pill hid its "Ctrl K" from its name (the voice command "click Ctrl K" still matched
  nothing); the key cap's tooltip now equals its name, so it is not read twice as a description.
- listNav's comment still cited DataTable's two layouts as the reason for its visibility filter.

frontend/src/lib/listNav.ts

@@ -66,8 +66,8 @@ function itemAt(list: NavList, index: number): HTMLElement | null {
 function ordered(): NavList[] {
   return (
     [...lists.values()]
-      // Only lists on screen: a responsive table renders its rows twice — a table and a card list, one
-      // of them display:none at any width (ui/DataTable) — and `j` must not walk into the hidden copy.
+      // Only lists on screen: a list can be mounted yet hidden (display:none in a collapsed panel or
+      // an inactive tab), and `j` must not walk into rows nobody can see.
       .filter((l) => l.el.isConnected && l.el.checkVisibility?.() !== false)
       .sort((a, b) =>
         a.el.compareDocumentPosition(b.el) & Node.DOCUMENT_POSITION_FOLLOWING ? -1 : 1,

frontend/src/lib/useFocusKeeper.restore.dom.test.tsx

@@ -61,4 +61,26 @@ describe("Back from a sub-view whose held control the swap removed", () => {
       document.activeElement?.closest("[data-nav-index]")?.getAttribute("data-nav-index"),
     ).toBe("2");
   });
+
+  it("leaves the focus alone once the reader has used the stand-in", async () => {
+    render(<Page />);
+    button("c").focus();
+    const pos = navPosition()!;
+    act(() => show("detail"));
+    button("Back to library").focus();
+
+    act(() => show("grid"));
+    await act(() => Promise.resolve()); // the keeper places its stand-in
+    const standIn = document.activeElement;
+    expect(standIn?.textContent).toBe("a");
+    // A key typed into it fires no focusin — but it is the reader's focus now.
+    act(() => {
+      standIn!.dispatchEvent(new KeyboardEvent("keydown", { key: "x", bubbles: true }));
+    });
+    const cancel = restoreNavPosition(pos);
+    await wait(120);
+    cancel();
+
+    expect(document.activeElement).toBe(standIn);
+  });
 });

frontend/src/lib/useFocusKeeper.ts

@@ -70,6 +70,12 @@ export function useFocusKeeper(ref: RefObject<HTMLElement | null>): void {
       if (t !== standIn) standIn = null;
       held = t && root.contains(t) && !t.closest("[data-nav-index]") ? t : null;
     };
+    // Using the stand-in makes it the reader's own focus: a click on it or a key typed into it fires
+    // no focusin, and a restore still polling for its list would otherwise take the focus from
+    // under the reader's hands.
+    const onUse = () => {
+      standIn = null;
+    };
     const watch = new MutationObserver((records) => {
       const lost = held;
       if (!lost || lost.isConnected) return;
@@ -86,9 +92,13 @@ export function useFocusKeeper(ref: RefObject<HTMLElement | null>): void {
       }
     });
     document.addEventListener("focusin", onFocusIn);
+    document.addEventListener("pointerdown", onUse, true);
+    document.addEventListener("keydown", onUse, true);
     watch.observe(root, { childList: true, subtree: true });
     return () => {
       document.removeEventListener("focusin", onFocusIn);
+      document.removeEventListener("pointerdown", onUse, true);
+      document.removeEventListener("keydown", onUse, true);
       watch.disconnect();
     };
   }, [ref]);