dsh-space-plan2: Small-Apartment Space Utilization Plan Generator Plugin

`dsh-space-plan2` is a plugin in the DeepSeek Harness (DSH) ecosystem that adds small-unit space planning capabilities to agents. It is implemented in pure Node, has no network dependencies, and focuses on generating space utilization plans based on parameters. After installation, it can be invoked directly through the `space_plan2` tool. It is suitable for integration into relevant workflows and depends on `@deepseek-ai/cordis` and `@deepseek-ai/dsh-tools`.