Handle left over threads from deleted assistants better

[sheng-liang]

Right now if I delete an assistant, its threads remain. When I click on these threads, I get an error "Assistant not found..."

At the very least it should tell me the name of the assistant it cannot find.

If we store the chat thread with the assistant, perhaps we should just delete or gray out the threads?

If the chat threads remain in the DB anyway, should we show the threads even after the assistant is deleted?

[cjellick]

My thought is that I'd rather not auto-delete the thread in case the user wants to copy some texts out of it. I'd like it to be marked as read-only basically

[cjellick]

going to live with this for now so that we can shift focus