Create a Stripe webhook handler in Next.js

Write a complete Next.js App Router Route Handler (route.ts) for Stripe webhooks. The handler should: 1. Verify the signature securely using the stripe library and STRIPE_WEBHOOK_SECRET. 2. Handle these specific event types: checkout.session.completed, invoice.payment_succeeded, customer.subscription.deleted. 3. Update the database using Prisma to set the user's tier, subscription status, and stripe client details. 4. Log events cleanly and return proper HTTP status codes. Provide the complete code block.