dsh-refined: Provides Obsidian Border style theme and Markdown beautification for DSH frontend

dsh-refined is a pure front-end browser extension designed for the DeepSeek Harness (DSH) interface, aiming to port the effects of DeepSeek-Refined to the DSH Web platform. It does not modify source code or inject scripts, primarily addressing two major issues: inconsistent global color schemes across the DSH interface and a lack of visual hierarchy in Markdown. The plugin offers five themes, including Border and Nord, supports automatic switching between light and dark modes, and achieves unified global color schemes by overriding CSS variables. Core features include beautifying Markdown elements (such as vertical bars for headings, dot-matrix backgrounds for blockquotes, and independent coloring for bold, italic, and code text), and providing a palette button in the session header for quick theme switching. Theme selections are saved in the browser's localStorage and persist after restart.