dsh-better-ux: UI Optimization Plugin for DeepSeek Harness

`dsh-better-ux` is a web UI optimization plugin for DeepSeek Harness (DSH). It aims to address the limitations of the original interface in multi-session management and mobile interactions, improving efficiency through independent modules. Core features include optimized quick actions in session rows, model selection as a full-screen overlay to reduce UI hierarchy, in-depth mobile enhancements (custom navigation bar, image sending, and no autofocus), and global font scaling settings. It does not change core logic, is compatible with `dsh-vision-router`, and must be manually enabled in settings after installation.