dsh-html-decode: HTML Unescape Utility

`dsh-html-decode` is a DeepSeek Harness plugin implemented in pure Node.js for efficiently performing HTML character entity decoding in the DSH environment, converting entities such as `&amp;` into `&` or `<`. This plugin has no network dependencies, relies on `@deepseek-ai/cordis` and `@deepseek-ai/dsh-tools`, and is suitable for processing text streams containing escaped characters, such as web content and logs. Once installed, its related tools can be invoked within a session.