dsh-plugin-canvas: HTML Design Prototype Preview and Privacy Protection in DeepSeek Harness

`dsh-plugin-canvas` is an open-source plugin for DeepSeek Harness that solves the problem of developers needing to switch between applications to preview HTML design mockups. The plugin provides a native Canvas tab, supporting instant preview, privacy blur overlays, and sandboxed rendering. It currently only supports Windows. After installation, users can load HTML files in DSH and apply blur effects, although the blur only applies to the current session.