fix(ui): stable shelf-card menu triggers, a named Button by type, true layout comments

- Home's rail handed each card a fresh `() => menu.triggerProps(c)` per
  render, defeating memo(VideoCard) on every tile whenever the menu's own
  state changed. `useItemTriggers` (ui/useContextMenu) keeps one trigger per
  item, index-aligned; tested for identity across renders.
- The Button accessible-name union had one hole: `<Button icon={…} />` with
  no children and no size typechecked into a nameless button. A textful
  button now needs children or a name; pinned with @ts-expect-error.
- comfortPin's header said the pin belongs "on every card and row", which
  the code never meant (an episode, a season, a person are not pin kinds).
  It now says what is pinnable — and the show page's Related strip, whose
  shows ARE pinnable, gets the pin menu it was missing (and a rem width).
- gridColumns / feedView / VirtualGrid claimed layouts 1024–2560 are
  "byte-identical" under the column cap; the small cards are capped at 2560
  with the filter rail collapsed. The comments say so.

frontend/src/components/ui/VirtualGrid.tsx

@@ -47,8 +47,8 @@ export interface VirtualGridProps<T> {
    * just above its minimum column, so on an ultrawide it answers "more room" with more, smaller
    * items forever — 3440px gave the feed 11 columns of 264px. With a cap the extra width goes into
    * the items instead (8 columns of ~370px), which is what a screen watched from a distance wants.
-   * It only ever binds ABOVE the width where that many columns already fit, so narrower layouts —
-   * including the 1024px floor and 1920/2560 — are untouched. */
+   * It only ever binds ABOVE the width where that many columns already fit, so the 1024px floor and
+   * 1920 are untouched; at 2560 it depends on the caller's cap (see `feedView.maxCols`). */
   maxCols?: number | null;
   /** Estimated row height before measurement; real heights are measured per-row, so this only
    * affects the very first paint and the scrollbar's initial guess. Measure it, don't guess — a