Replace the default Diff rendering of DeepSeek Harness with dsh-diff-viewer

DSH-Diff-Viewer is a web interface enhancement plugin for DeepSeek Harness maintained by lehhair. It takes over the write/edit tool bar via the keyed slot of ui-tool, and replaces the default DiffBlock with a PiUI-style DiffViewer. This article verifies its mechanism, functions and installation method by cross-checking with the community directory page and GitHub repository: please use the Release tarball to install into the web profile, do not directly install the source code from GitHub; uninstallation will restore the official toolbar. The plugin runs with the current DSH process permissions, and the source code and BSD-3-Clause license statement should be checked before installation.