dsh-platform-fee: Food Delivery Platform Commission Calculation Plugin

The DeepSeek Harness (DSH) plugin `dsh-platform-fee` provides a local solution for calculating food delivery platform fees. Maintained by uckkk and implemented with pure Node.js, it requires no network requests, performs precise calculations based on parameters, and returns detailed results. Once installed, it can be invoked directly in a session, making it suitable for scenarios that require local fee processing and prioritize stability.