2026heshao/dsh-forget-session

Adds a Forget action to every session row menu, confirmed by a second click in the menu, that removes the session from the sidebar and from disk: running work is stopped, workspace, archive and pin records are detached through official channels, the log directory and projection-cache entries are deleted, and a revive guard re-deletes anything a late write or a lingering handle recreates; memories, attachments and other sessions are left alone.