dsh-turn-marks: Add a Claude Code-style session message bar to DSH Web UI.

# Introduction When debugging agents using DeepSeek Harness (DSH), a single conversation often involves dozens of turns. To review a previously sent instruction, you must scroll through the conversation flow; the longer the history, the harder it is to locate the specific point. Claude Code and Codex desktop applications feature a row of "turn marks" along the left edge of the conversation—one for each message—which allows you to jump to that point with a single click. This interaction is currently missing in the DSH Web UI. The dsh-turn-marks introduced below fills this gap: it adds a row of message bars to the left edge of the conversation without modifying native components, providing jump functionality, previews, and position indicators. # What is this dsh-turn-marks is a DSH Web plugin maintained by magicOF2.