Add ability to purge historical sessions in batch​

As shown in the figure, currently only one conversation can be deleted at a time. It will be very troublesome if there are too many conversations. Could you support the function of selecting multiple conversations for batch deletion?

<img width="446" height="589" alt="image" src="https://github.com/user-attachments/assets/4e5cb489-6f9b-432e-895b-cb3c12f954bc" />