dsh-theme-mist: Adds a hot-swappable client theme to DeepSeek Harness

dsh-theme-mist is a visual theme plugin for the DeepSeek Harness client, maintained by ffyfox, used for both desktop and web versions. It ported the color palette, material, and rounded corner language from the DSH Go reference design, featuring six built-in accent colors—misty blue, cyan, twilight purple, turquoise, amber, and graphite—combined with light/dark/system themes, all of which pass WCAG AA contrast validation. The left sidebar offers both glass and tiled materials, while the bottom input area features a floating frosted glass effect. All toggles are embedded within the official settings panel, requiring no manual configuration file editing, and leave no residual traces after uninstallation. The article provides instructions for both desktop plugin installation and web command-line installation, along with explanations of settings, uninstallation methods, and the pnpm verify local verification process.