dsh-codex-project: DSH Workspace Shared Subdirectory Plugin

The DeepSeek Harness plugin `dsh-codex-project` addresses the permission-management dilemma in cross-directory project development. Through the GUI, command line, or model tools, it allows a workspace to mount any number of shared subdirectories (with cross-drive support) while maintaining `workspace-write` permissions throughout, eliminating the need to escalate to the high-risk `danger-full-access` permission. Leveraging the Cordis framework, the plugin implements runtime security and data persistence via HTTP routing, context injection, tool registration, scoped tokens, and filesystem isolation. It provides developers with an efficient and secure modular development environment.