fix(bot): remove serialize_user_updates from on_text to unblock UI

- Remove @serialize_user_updates from on_text in bot_handlers.py
- on_text holds the per-user lock for 5-10s during AI generation,
  blocking all button/callback handlers for the same user
- Keep @serialize_user_updates on all fast handlers (settings, chats,
  connect, disconnect, status) where race conditions on DB writes
  are the real concern

Author: oponfil

handlers/bot_handlers.py

@@ -52,7 +52,6 @@ async def on_start(update: Update, context: ContextTypes.DEFAULT_TYPE) -> None:
     await update_user_menu(context.bot, u.id, u.language_code, is_connected)
 
 
-@serialize_user_updates
 @typing_action
 async def on_text(update: Update, context: ContextTypes.DEFAULT_TYPE) -> None:
     """Обработчик текстовых сообщений — генерирует ответ через ИИ."""