DeepSeek Harness Plugin: dsh-session-rename

The `dsh-session-rename` plugin addresses the issue that models in DeepSeek Harness (DSH) cannot directly manage session titles. It provides the `rename_session` tool, enabling the Agent to explicitly rename a session based on conversational context. The plugin offers zero runtime dependencies, title pinning, and privacy protection (titles are not included in model inputs). After installation, rules need to be defined in `AGENTS.md`, with the model deciding when to invoke the tool. Note that only loaded sessions can be modified, and the semantic processing of titles is handled by `@deepseek-ai/dsh-session-title`.