dsh-japan: Japan Country Information Query Plugin

dsh-japan is a pure Node.js plugin designed specifically for DeepSeek Harness (DSH) to retrieve Japanese country metadata locally. It has no network dependencies and provides two functions: fetching complete information (such as capital, currency, etc.) and querying individual items. It is suitable for scenarios that require stable and fast access to Japan-related information while avoiding frequent network requests, and it runs stably and is open source.