add-plugin

Use this skill when the user wants to add, refactor, or generalize a agentpay <plugin> integration like Bitrefill. Follow the shared plugin registration path under src/plugins, keep plugin-specific API or scraping code under src/lib/<plugin> or src/lib/<plugin>/, reuse the existing Rust daemon signing and policy path through the shared CLI plugin context instead of reimplementing signing, and add focused CLI tests…