refactor(pins): drop the unused ComfortPinMenu and the comment that described it

Every surface composes the pin row into its object's one action list (E28 C1); the pin-only menu
had no caller left. Also un-exports isStandInFocus, which only its own file reads since H1.

frontend/src/components/comfortPin.tsx

@@ -15,13 +15,12 @@ import { type ActionMenuItem } from "./ui/ActionMenu";
 // shown — a video, a channel, a playlist, a Plex show or movie: you decide something is comfort media
 // while you are watching it. (Locked decision 3: an episode, a season and a person are not pin kinds,
 // so their cards and strips carry no pin.) This file is the one place the pin lives; every surface
-// composes the same `ActionMenuItem` into the menu it already has (`Playlists`, `PlaylistsRail`) or
-// mounts the `ComfortPinMenu` wrapper when it has none.
+// composes the same `ActionMenuItem` into its object's ONE action list (E28 C1): the video, Plex and
+// channel actions (`useVideoActions`, `usePlexCardActions`, `Channels`), the playlist rail and page,
+// and Home's shelves. There is no pin-only menu any more.
 //
 // Feature layer, not `components/ui/`: it speaks a domain API slice, which the platform boundary
-// (eslint `no-restricted-imports`) forbids a `ui/` primitive from doing. The MENU SURFACE that
-// renders this item lives in `ComfortPinMenu.tsx` — the same hook/component split, for the same
-// react-refresh reason, as `useContextMenu.ts` beside `ContextMenu.tsx`.
+// (eslint `no-restricted-imports`) forbids a `ui/` primitive from doing.
 
 /** What the API needs to pin something: the kind, and the id the rest of the API already speaks for
  *  that kind (a video id, a channel id, a Plex `rating_key`, a playlist id). Mirrors