Castor6/dsh-auto-workspace

Project-less chats for dsh: a session created without a workspace gets its own directory under ~/Documents/DSH/<date>/chat-NN, reused whenever the chat is reopened and left in Ungrouped rather than made a sidebar project; the new-session hero gains a hover clear badge and a "work without a project" row, and a client-only sentinel workspace keeps that hero and its composer usable.