chore(deps-dev): bump next from 15.4.8 to 16.1.5 in /internal/site

Bumps [next](https://github.com/vercel/next.js) from 15.4.8 to 16.1.5.
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](vercel/next.js@v15.4.8...v16.1.5)

---
updated-dependencies:
- dependency-name: next
  dependency-version: 16.1.5
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

internal/site/package.json

@@ -60,7 +60,7 @@
     "lexical": "^0.32.1",
     "lucide-react": "^0.507.0",
     "mermaid": "^11.7.0",
-    "next": "15.4.8",
+    "next": "16.1.5",
     "next-auth": "^5.0.0-beta.29",
     "next-themes": "^0.4.6",
     "postcss": "^8.5.3",