perf: skip ffmpeg transcode for PocketTTS streaming — use WAV directly

PocketTTS emits 16-bit PCM WAV (16 kHz mono). WAV is natively supported
on all browsers including iOS/macOS Safari, so the ffmpeg MP3 transcode
is unnecessary for the streaming path.

Using format=wav for PocketTTS voices eliminates the ffmpeg subprocess
startup delay (~200–400 ms) and a pipeline stage, giving lower latency
to first audio frame. Kokoro and CF AI continue using MP3 (they output
MP3 natively or via the OpenAI-compatible endpoint).

The runner (MinIO storage) is unaffected — it still stores MP3 for
space efficiency.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ui/messages/ru.json

@@ -302,6 +302,24 @@
   "book_detail_range_queuing": "В очереди…",
   "book_detail_scrape_range": "Диапазон глав",
   "book_detail_admin": "Администрирование",
+  "book_detail_admin_book_cover": "Обложка книги",
+  "book_detail_admin_chapter_cover": "Обложка главы",
+  "book_detail_admin_chapter_n": "Глава №",
+  "book_detail_admin_description": "Описание",
+  "book_detail_admin_chapter_names": "Названия глав",
+  "book_detail_admin_audio_tts": "Аудио TTS",
+  "book_detail_admin_voice": "Голос",
+  "book_detail_admin_generate": "Сгенерировать",
+  "book_detail_admin_save_cover": "Сохранить обложку",
+  "book_detail_admin_saving": "Сохранение…",
+  "book_detail_admin_saved": "Сохранено",
+  "book_detail_admin_apply": "Применить",
+  "book_detail_admin_applying": "Применение…",
+  "book_detail_admin_applied": "Применено",
+  "book_detail_admin_discard": "Отменить",
+  "book_detail_admin_enqueue_audio": "Поставить в очередь",
+  "book_detail_admin_cancel_audio": "Отмена",
+  "book_detail_admin_enqueued": "В очереди {enqueued}, пропущено {skipped}",
   "book_detail_scraping_progress": "Загружаются первые 20 глав. Страница обновится автоматически.",
   "book_detail_scraping_home": "← На главную",
   "book_detail_rescrape_book": "Перепарсить книгу",