dsh-rich-context: Agent Instruction Manager for DeepSeek Harness

The `dsh-rich-context` plugin provides a visual Agent instruction management interface for DeepSeek Harness (DSH), addressing the issue of fragmented instruction files across multiple tools. Located in the Skill Center sidebar, the plugin allows users to edit instruction files under the **Global** and **Workspace** tabs and supports custom path management. Its core features include cross-tool directory scanning (supporting 10 tools) to locate instruction files and “Set as default,” which creates symbolic links for scanned files to simplify routing logic. Developed with a front-end/back-end separated architecture, the plugin requires restarting the `dsh web` process after installation to take effect.