a history navigator for deepseek-harness

Key features

• A bar = round dialogueNavigate by user message instead of a tool-separated Asistant step navigation
• IncludeVisible Reply Text, Markdown Preview, Round Jump
• Once the page is refreshed, a navigation bar should appear on the right side of the long conversation
• Suspend or previewshow the Markdown response after rendering, quickly judge whether this round is worth looking back