dsh-font-customizer: DeepSeek Harness UI and Code Font Customization Plugin

DeepSeek Harness (DSH) introduces the dsh-font-customizer plugin, designed to address users' needs for personalized UI and code fonts. The plugin allows users to independently configure UI font stacks and monospaced code fonts, and provides fine-grained body font size adjustment from 12 to 17 px. Its core strengths include local font detection and scanning, built-in presets for popular fonts, and customization through CSS font stacks. Settings are written atomically to local storage, enabling automatic cross-device synchronization and one-click reset.