dsh-spec-panel: DSH Sidebar OpenSpec Workbench

`dsh-spec-panel` is a DeepSeek Harness (DSH) sidebar plugin designed to standardize a "write specs first, then implement, then verify" development workflow using the OpenSpec standard directory structure. It maintains no additional state and reads and writes real files directly within the workspace, providing source-of-truth browsing, a change workbench, status inference, and real-time checklist item selection. It supports one-click generation of change directories from templates and allows artifacts to be opened directly in the sidebar's built-in editor.