dsh-memoryhub: Integrate MemoryHub project memory into DeepSeek Harness

dsh-memoryhub is an MIT-licensed plugin for DeepSeek Harness (dsh), designed to address the issue of project memory usage across sessions. It integrates the `.memoryhub/` checkpoint memory maintained by MemoryHub into dsh sessions, supporting bidirectional data synchronization: automatically loading checkpoint memory upon session startup, while also allowing the current session to be saved back to MemoryHub via the `mh_save` command. The plugin registers six core tools (such as `mh_load`, `mh_save`, `mh_status`, etc.) and the `mh` workflow skill, providing a Memory tab in the Web UI for visualizing checkpoints.