react and react-dom are optional peers but plot() and legend() need them #175

plot() (src/plotDom.ts on main) and legend() (src/legends.js) render through react-dom/server's renderToStaticMarkup, but package.json marks react and react-dom as optional in peerDependenciesMeta. Installing the package without React and calling Plot.plot() or Plot.legend() fails at runtime.

Fix: make react and react-dom required peers by removing them from peerDependenciesMeta.