Linusteller/dsh-session-delete

Adds a red "Delete session" item beneath "Archive" in the sidebar session menu, with a custom confirmation dialog, for real session deletion — stops the session's running work, detaches its workspace, archive and pin accounting, removes its projection cache and log directory, then broadcasts removal so the row disappears at once, instead of only archiving it. Session deletion removes the conversation from disk permanently and cannot be undone.