DeepSeek Harness chat history and session management: search archives, restore conversations, and delete safely

DSH 设置面板会话管理器：归档 / 恢复 / 彻底删除 / 移动到其他工作区，带工作区标签与会话日期；统一「会话管理」面板。Session manager for the DeepSeek Harness settings panel — archive / restore / permanently delete / move sessions across workspaces, with workspace tags & session dates in one unified panel.