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/Toaster.tsx

@@ -125,6 +125,8 @@ export default function Toaster({
     // as a toast was up (the connection notice: until the server answered). The same rung UpNextCard
     // uses for the same reason. Clicks between the cards go through to what is underneath.
     <div
+      // lib/listNav: focus on a toast's Undo is not the reader leaving the list the toast is about.
+      data-toast-region=""
       aria-live={isTop && armed ? "polite" : "off"}
       className={`absolute left-4 z-overlay flex flex-col gap-2 w-80 max-w-[calc(100vw-2rem)] ${
         overlay ? "bottom-24 pointer-events-none" : "bottom-4"