dsh-session-retitle: DeepSeek Harness Session Renaming Plugin

`dsh-session-retitle` is a plugin for DeepSeek Harness (DSH) designed to address the limitation that the official interface assigns a session title only once automatically and does not update it in subsequent conversations. It adds a rename button to the session header, supporting either automatic generation of a short Chinese title when left blank or manual specification. With zero runtime dependencies, it calls the official service and includes theme adaptation, concurrency protection, and fault tolerance. After installing it via `pnpm`, users can flexibly manage session names without affecting archived historical sessions.