dsh-ctr-significance: CTR Significance Calculation Plugin

The `dsh-ctr-significance` plugin provided by DeepSeek Harness (DSH) locally calculates the statistical significance of conversion rate differences. It does not require internet access, is built with Node.js, and supports precise parameter-based calculations while returning detailed results. Developers can install the plugin and call the `ctr_significance` tool to quickly verify effect differences in model inference or experimental comparisons locally.