dsh-one-dark-pro: One Dark Pro Color Scheme and Appearance Toggle

The DSH (DeepSeek Harness) plugin `dsh-one-dark-pro` introduces the One Dark Pro color scheme to the DSH environment and expands the appearance options into a four-option grid: Light, Dark, System, and One Dark Pro. The plugin is implemented through two parts, Host and Client: Host registers the settings namespace and routes, while Client overrides the default options and renders the theme. To install it, add the dependency and bundles configuration to the profile's `package.json`, then restart `dsh web`. Users can select a theme in the settings, and the preference is persisted to `~/.dsh/settings.yaml`.