fix(keys): epic-end review round 3 — the part-way clip count shows, busy buttons keep focus, cards say their names

Targeted round over 3cd0c525's fix surfaces: 14 raised, 14 fixed.

- VideoEditor: the "only X of Y clips" toast went silent exactly on the job-cap/quota refusal it was
  written for (req had already reported the error); it now always shows. The cut list holds still while
  Create queues, and a retry continues the "(i/N)" series.
- ChannelPage: Subscribe/Unsubscribe use Button `loading`, "Load more" and ChannelDiscovery's Subscribe
  block the click with aria-disabled instead of native disabled; busy Block/Hide no longer light up on
  hover.
- listNav: an item can name itself (`navItemAttrs(i, name)`) — Plex posters, seasons, episodes, message
  rows and download rows pass their title; focus on a toast's Undo keeps the removed card's slot.
- AnchoredPopover: the hand-back only for focus-managed surfaces (a hover card no longer pulls focus
  back); the dead panel-ref check is gone.
- AccountPanel: no confirmation mail offered to the demo account; send_failed copy no longer blames
  the message for an unreachable server. Pager comment points at scrollParent.

frontend/src/components/ui/Pager.tsx

@@ -49,7 +49,7 @@ export default function Pager({
   // Turning the page — or resizing it, which re-slices from a different first item — swaps the whole
   // list, so put the reader at its top; landing mid-list in a page you haven't seen is disorienting.
   // The page scroller is the app's <main> (PageScroller documents itself as the ONE scroller; the
-  // same implicit contract BackToTop and VirtualGrid's getScrollParent already rely on).
+  // same implicit contract BackToTop and lib/listPaging's scrollParent (VirtualGrid, listNav) already rely on).
   function scrollListToTop() {
     document.querySelector("main")?.scrollTo({ top: 0 });
   }