dsh-greet: A Minimal Plugin for Registering the Greet Tool

The DSH Harness (DSH) plugin `dsh-greet` is a minimal reference implementation that demonstrates how to write a pure JavaScript plugin and publish it to GitHub. It requires no build step and registers the `greet` tool for direct agent invocation through `cordis.patch.yml` configuration. The plugin depends on `@deepseek-ai/dsh-tools` and `@deepseek-ai/cordis`, runs with the current process permissions, and is suitable for developers to quickly validate development workflows or integrate lightweight functionality. Installation and removal are both completed via the command line.