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/Button.dom.test.tsx

@@ -161,6 +161,9 @@ describe("Button accessible-name contract (type level)", () => {
         <Button size="icon" icon={<span />} data-testid="bad-a" />
         {/* @ts-expect-error iconOnly with no label/aria-label/title has no accessible name */}
         <Button iconOnly icon={<span />} data-testid="bad-b" />
+        {/* @ts-expect-error an icon with no children and no size renders no text and no name */}
+        <Button icon={<span />} data-testid="bad-c" />
+        <Button icon={<span />} label="an icon button named by label" />
         <Button size="icon" icon={<span />} label="by label" />
         <Button size="icon-sm" icon={<span />} aria-label="by aria-label" />
         <Button iconOnly icon={<span />} title="by title" />