DSH Plugin: dsh-teaching-board

`dsh-teaching-board` is an educational plugin for DeepSeek Harness that projects Agent-generated HTML into an interactive “board” interface. Users can annotate the board, capture screenshots, and provide feedback, while the Agent can also proactively view snapshots. The plugin supports ink anchoring (scrolling with content) and incremental updates (preserving scroll position and animations). Through the `open`, `append`, `set`, and `remove` parameters of the `stage_panel` tool, the board can evolve through multiple iterations. Screenshot capture is limited to the active tab, and any image exceeding 1.2 MB automatically falls back to JPEG.