Bump react from 18.3.1 to 19.1.0 in /src/Elastic.Documentation.Site

Bumps [react](https://github.com/facebook/react/tree/HEAD/packages/react) from 18.3.1 to 19.1.0.
- [Release notes](https://github.com/facebook/react/releases)
- [Changelog](https://github.com/facebook/react/blob/main/CHANGELOG.md)
- [Commits](https://github.com/facebook/react/commits/v19.1.0/packages/react)

---
updated-dependencies:
- dependency-name: react
  dependency-version: 19.1.0
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

src/Elastic.Documentation.Site/package-lock.json

@@ -44,7 +44,7 @@
     "postcss-import": "16.1.0",
     "prettier": "3.5.3",
     "prettier-plugin-tailwindcss": "0.6.12",
-    "react": "^18.3.1",
+    "react": "^19.1.0",
     "react-dom": "^18.3.1",
     "typescript-eslint": "8.33.1"
   },