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

Unified DSH checkpoints: session + workspace + config three-state snapshots with one-shot rollback — /checkpoint and /rewind commands, a checkpoint tool, automatic interval snapshots, a Settings page timeline with pairwise diffs, and seed-replay session r

DSH 会话管理插件：删除（回收站恢复/彻底清除）、统计、继续/暂停、打开日志目录、对话顶部抽屉、工作区分组与排序、上下文压缩阈值设置。DSH session manager: delete with trash/restore/purge, stats, continue/pause, log folder, header drawer, workspace grouping, context compaction threshold.