Motivation

• Include the Stripe package so serverless API deployments can resolve require('stripe') and stop /api/admin/create-checkout-session returning 500 due to a missing module.
• Preserve server-side-only usage and the existing secret-key validation that rejects missing keys and keys starting with pk_.

Description

• Add "stripe": "^18.3.0" to root dependencies in package.json.
• Add stripe to the root dependency map in package-lock.json so lock metadata reflects the new dependency.
• Do not change lib/stripe-client.js behavior; the STRIPE_NOT_CONFIGURED and STRIPE_SECRET_KEY_INVALID guards remain intact.
• No checkout or business-logic changes were made beyond ensuring the package is declared.

Testing

• Ran npm test and all tests passed (110 passed, 0 failed).
• Ran cd examples/webhook-auto-verify && npm run check and the script completed successfully.
• Attempted npm install stripe --save but registry access was blocked with HTTP 403, so the dependency and lockfile were updated directly and tests were still green.

Codex Task