i18n(dictation): add "Dictation" aria-label key to en-US + ru-RU (#314 F6)

The F4 fix introduced t("Dictation") as the neutral aria-label for a disabled
mic with no reason (reachable via the AI chat mic while the assistant streams),
but the key wasn't in either locale — a ru-RU screen-reader user would hear the
English "Dictation". Add it to both locales.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/client/public/locales/en-US/translation.json

@@ -1274,6 +1274,7 @@
   "Voice dictation is not configured": "Voice dictation is not configured",
   "Microphone is unavailable or already in use": "Microphone is unavailable or already in use",
   "Audio recording is not available in this browser/context": "Audio recording is not available in this browser/context",
+  "Dictation": "Dictation",
   "Dictation becomes available once the page finishes connecting": "Dictation becomes available once the page finishes connecting",
   "No connection to the collaboration server — dictation unavailable": "No connection to the collaboration server — dictation unavailable",
   "This page is read-only": "This page is read-only",

apps/client/public/locales/ru-RU/translation.json

@@ -400,6 +400,7 @@
   "Microphone is unavailable or already in use": "Микрофон недоступен или уже используется",
   "Could not start recording": "Не удалось начать запись",
   "Audio recording is not available in this browser/context": "Запись аудио недоступна в этом браузере/контексте",
+  "Dictation": "Диктовка",
   "Dictation becomes available once the page finishes connecting": "Диктовка станет доступна после подключения к документу",
   "No connection to the collaboration server — dictation unavailable": "Нет связи с сервером совместного редактирования — диктовка недоступна",
   "This page is read-only": "Страница открыта только для чтения",