feat: Stripe integration — checkout + webhook + subscription lifecycle

- src/lib/stripe/index.ts: Stripe client (checkout session + webhook event)
- POST /api/aos/stripe/checkout: create subscription checkout for a license
- POST /api/aos/stripe/webhook: handle events:
  - checkout.session.completed → link Stripe customer/subscription to license
  - invoice.paid → activate license (remove trial)
  - customer.subscription.deleted → cancel license + schedule instance deletion
  - invoice.payment_failed → suspend license (dunning)
- Middleware: stripe/webhook is public (Stripe calls it without auth)
- stripe package installed (v23)

package.json

@@ -82,6 +82,7 @@
     "recharts": "^2.15.4",
     "sharp": "^0.34.3",
     "sonner": "^2.0.6",
+    "stripe": "^23.0.1",
     "tailwind-merge": "^3.7.0",
     "tailwindcss-animate": "^1.0.7",
     "uuid": "^11.1.0",