dsh-line-select: Select code by line and inject into agent in DSH Web

dsh-line-select is a line selection plugin for DeepSeek Harness Web, designed to address the pain point where Agents must read entire files or manually append line numbers when modifying code. The plugin provides a visual panel above the input box, supporting workspace file browsing, code preview with line numbers, and intuitive selection of start and end lines by clicking. Upon selection, the plugin generates a reference such as `@path:start-end` and writes it to the draft; before sending, the Host automatically expands this reference, injecting the original text of the specified line range into the context. This enables the Agent to precisely modify specific code segments without needing to read the file itself. Additionally, it supports whole-file references and manual reference input. Installation requires only using the `dsh plugin` command to add the local path and restart the Web service, with no third-party runtime dependencies.