dsh-web-close: The Persistent Close Button in the DSH Web Interface

`dsh-web-close` is a web plugin for DeepSeek Harness (DSH) that provides a persistent close button. It supports drag-based positioning and position memory, and safely exits processes through graceful mechanisms (`appExit`, `SIGINT`). The plugin relies on MIT-licensed dependencies, is implemented in pure native DOM, and is effective only for the web profile.