Update react monorepo to v19

Author: renovate[bot]

package-lock.json

@@ -11,8 +11,8 @@
   "dependencies": {
     "markdown-to-jsx": "^7.4.7",
     "next": "15.5.2",
-    "react": "^18.3.1",
-    "react-dom": "^18.3.1"
+    "react": "^19.0.0",
+    "react-dom": "^19.0.0"
   },
   "devDependencies": {
     "@stackbit/cms-contentful": "^1.0.0",