feat: Add Stripe provider implementation with webhook support

- Implement Stripe payment provider with PaymentIntent creation
- Add webhook handler with signature verification and event processing
- Handle payment status updates and refund events
- Move Stripe to peer dependencies for better compatibility
- Update README with peer dependency installation instructions
- Document new provider configuration patterns and webhook endpoints

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

package.json

@@ -100,16 +100,17 @@
     "rimraf": "3.0.2",
     "sharp": "0.34.2",
     "sort-package-json": "^2.10.0",
+    "stripe": "^18.5.0",
     "typescript": "5.7.3",
     "vite-tsconfig-paths": "^5.1.4",
     "vitest": "^3.1.2"
   },
   "peerDependencies": {
     "@mollie/api-client": "^3.7.0",
-    "payload": "^3.37.0"
+    "payload": "^3.37.0",
+    "stripe": "^18.5.0"
   },
   "dependencies": {
-    "stripe": "^14.15.0",
     "zod": "^3.22.4"
   },
   "engines": {