Add Subscription Billing to React

# Install

npm install @paylio/react

// PricingPage.tsx

import { PaylioPricingGrid } from "@paylio/react";

export default function PricingPage() {
  return (
    <PaylioPricingGrid
      publishableKey="pk_live_xxx"
      userId="user_123"
      theme="light"
      onSubscribed={(sub) => {
        console.log("Subscribed to", sub.plan.name);
      }}
    />
  );
}