dsh-airport-time: Airport Advance Arrival Time

The `dsh-airport-time` plugin for DeepSeek Harness (DSH) is designed to efficiently calculate airport lead time locally. Its core features include precise, parameter-based calculation and detailed result output. It is implemented in pure Node.js and has no network dependencies. Installation requires the `dsh plugin add` command and depends on a specific version of the core library. This plugin is suitable for scenarios with zero network dependencies, but it is recommended to review the source code and license before use.