Paddle Billing Integration Plugin

Drop-in Paddle Billing integration for Next.js applications. Handles the complete payment lifecycle: checkout session creation, webhook processing (transaction.completed, subscription events, refunds), customer portal management, and subscription status tracking. ### Included Files - lib/paddle/client.ts - Paddle API wrapper - lib/paddle/webhooks.ts - Typed webhook handlers - components/PaddleProvider.tsx - React component (Paddle.js v2) - components/CheckoutButton.tsx - One-click checkout button - app/api/checkout/route.ts - Checkout session API - app/api/webhooks/paddle/route.ts - Webhook receiver - schema.sql - DB schema for payments Supports both one-time purchases and recurring subscriptions.