dsh-molecule-viewer: Render interactive 3D molecular structures in DSH sessions

# Introduction For those working on protein structures or molecular docking, the typical workflow for viewing structures is: the model calculates the results, you save the PDB file, switch to PyMOL or a web tool to open it, and then take a screenshot to paste back into the discussion. Files are shuffled between the chat session and external software, requiring a context switch and interrupting your train of thought. In DSH (DeepSeek Harness), it is not difficult to have the model read a molecular file, but the challenge lies in making the structure itself appear in the session interface. The `dsh-molecule-viewer` plugin solves exactly this step: by passing a file path or molecular data, it renders a 3D molecular viewer directly in the session that supports rotation, zooming, and style switching. # What is it dsh-molecule-viewer is DS...