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/i18n/locales/en/errors.json

@@ -25,7 +25,7 @@
     "not_applicable": "This account has nothing left to confirm.",
     "not_approved": "Only an approved address can be invited.",
     "email_off": "No mail was sent: this instance has no working SMTP setup. Check Configuration → Email / SMTP.",
-    "send_failed": "The mail server didn't accept the message. Check Configuration → Email / SMTP, then try again.",
+    "send_failed": "The mail couldn't be sent: the mail server was unreachable, or it refused the login or the message. Check Configuration → Email / SMTP, then try again.",
     "demo": "The demo account is shared, so it can't get a set-password link."
   },
   "reason": {

frontend/src/i18n/locales/hu/errors.json

@@ -25,7 +25,7 @@
     "not_applicable": "Ezen a fiókon már nincs mit megerősíteni.",
     "not_approved": "Csak jóváhagyott címre küldhető meghívó.",
     "email_off": "Nem ment ki levél: ezen a példányon nincs működő SMTP. Nézd meg a Konfiguráció → E-mail / SMTP fület.",
-    "send_failed": "A levelezőszerver nem fogadta el a levelet. Nézd meg a Konfiguráció → E-mail / SMTP fület, majd próbáld újra.",
+    "send_failed": "Nem sikerült elküldeni a levelet: a levelezőszerver nem volt elérhető, vagy elutasította a belépést vagy a levelet. Nézd meg a Konfiguráció → E-mail / SMTP fület, majd próbáld újra.",
     "demo": "A bemutató fiók közös, ezért nem kaphat jelszóbeállító linket."
   },
   "reason": {