feat(design): a channel's and a Plex playlist's one action list (C1) — the row's "…", Delete + undo, an action toast's 8 s floor (E28 S3e2)

- Channels: the row's full-history, hide and unsubscribe buttons become its "…" at the row end
  (useChannelActions: open, pin, YouTube, copy name / link, full history or the admin reset,
  hide with an undo toast, unsubscribe behind its danger confirm); the card layout docks the "…"
  beside the name (ChannelLayoutGrid moreKey). The admin reset's confirm now names the reset.
- Plex playlist page: a title, a show group and a season each open the page's one row menu (a
  title's is its usePlexCardActions list plus the removal); no X at rest; removals take an undo
  toast whose Undo puts every row back at its own index in one request (bulk add `positions`);
  j/k walk the visible rows, Delete removes the walked one; rename and delete in the header's "…".
- notify: a toast with an action lives at least 8 s (the owner's call), whatever the toast setting.

frontend/src/lib/api/plex.ts

@@ -558,13 +558,16 @@ export const plexApi = {
       method: "POST",
       body: JSON.stringify({ title, item_rating_key }),
     }),
+  /** `positions` (one per key, an index over the ordered rows) puts removed rows back where they
+   *  stood — the list page's Undo, in one request; without it the keys are appended. */
   plexPlaylistAddBulk: (
     id: number,
     itemRks: string[],
+    positions?: number[],
   ): Promise<{ added: number; item_count: number }> =>
     req(`/api/plex/playlists/${id}/items/bulk`, {
       method: "POST",
-      body: JSON.stringify({ item_rating_keys: itemRks }),
+      body: JSON.stringify({ item_rating_keys: itemRks, ...(positions ? { positions } : {}) }),
     }),
   plexPlaylistRemoveBulk: (
     id: number,