build(deps): bump next from 15.0.3 to 15.1.2 in /examples/demo

Bumps [next](https://github.com/vercel/next.js) from 15.0.3 to 15.1.2.
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](vercel/next.js@v15.0.3...v15.1.2)

---
updated-dependencies:
- dependency-name: next
  dependency-type: direct:production
...

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

Author: dependabot[bot]

examples/demo/package-lock.json

@@ -49,7 +49,7 @@
     "gray-matter": "^4.0.3",
     "lodash": "^4.17.21",
     "lucide-react": "^0.453.0",
-    "next": "^15.0.1",
+    "next": "^15.1.2",
     "next-themes": "^0.3.0",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",