fix(ui): localise the confirm screen, drop the brand on the error state

The session-less /confirm page defaulted to English, so it showed the English
app title. Carry the recipient's language on the deeplink (?lang) and setLocale on
load so the page matches the email. Show a localised brand wordmark (Эрудит / Erudit,
matching the email) on the success state only; the invalid/expired state now shows
just the message, no header.

ui/src/lib/i18n/en.ts

@@ -4,6 +4,7 @@
 
 export const en = {
   'app.title': 'Scrabble',
+  'app.brand': 'Erudit',
   'dict.loading': 'Loading…',
   'connection.connecting': 'Connecting…',
 

ui/src/lib/i18n/ru.ts

@@ -5,6 +5,7 @@ import type { MessageKey } from './en';
 
 export const ru: Record<MessageKey, string> = {
   'app.title': 'Scrabble',
+  'app.brand': 'Эрудит',
   'dict.loading': 'Загрузка…',
   'connection.connecting': 'Подключение…',