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/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]);