plane-dsh-plugin: Sync DeepSeek Harness Sessions to Plane Project Management

`plane-dsh-plugin` is a native plugin designed specifically for DeepSeek Harness (DSH), aiming to bridge agent sessions with the Plane project management tool. It adopts a dual-end architecture and includes 8 built-in tools, supporting asynchronous synchronization of tasks, bugs, and progress to Plane after they are persisted in local SQLite, thereby avoiding blocking of main tasks. It provides a global floating panel, manual project switching, and a secure credential resolution mechanism. Installation requires fetching the bundle via NPM and configuring the API key and workspace information, making it suitable for developers who need to seamlessly integrate code development with project updates.