dsh-worktree: Git worktree filesystem isolation for DeepSeek Harness sub-agents

`dsh-worktree` is a plugin for DeepSeek Harness (DSH) designed to provide filesystem isolation for multiple sub-agents running in parallel via Git worktrees, preventing interference between working directories. It enables each sub-agent to share the repository object store while maintaining a separate workspace, primarily offering two entry points: the `ctx.worktree` service API and the `/worktree` slash command. Its core mechanism involves placing worktrees in the `.dsh/worktrees/<flatSlug>` directory and automatically creating the corresponding `worktree-<flatSlug>` branch. When creating, the plugin strictly validates the slug and attempts to perform environment configuration, such as copying configuration and linking dependencies. Regarding change protection...