dsh-project-context: Turn the DSH workspace folder into a project

`dsh-project-context` is an MIT-licensed DSH client plugin developed by buhuikongpan, designed to solve the problem of automatically acquiring a short "project workspace convention" after a model enters the workspace. The plugin treats sessions with a real current working directory (cwd) as projects. When a new session starts, it automatically injects an independent user message block (marked as `project-context`) via the `agent/pre-step` hook, without requiring manual prompt appending and without participating in system prompt concatenation. It is not applicable to system sessions without a cwd, and the interface supports both Chinese and English. The plugin provides a "Project" toggle switch on the right side of the input box, which is enabled by default. When disabled, the existing context block is not deleted but rendered as a "downgraded" status hint to prevent the model from mistakenly judging that the conventions have become invalid. The installation command is `dsh plu`.