chore(deps): bump next from 15.5.7 to 15.5.9 in /document (#6081)

Bumps [next](https://github.com/vercel/next.js) from 15.5.7 to 15.5.9.
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](https://github.com/vercel/next.js/compare/v15.5.7...v15.5.9)

---
updated-dependencies:
- dependency-name: next
  dependency-version: 15.5.9
  dependency-type: direct:production
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

document/package.json

@@ -18,7 +18,7 @@
     "fumadocs-ui": "15.6.3",
     "gray-matter": "^4.0.3",
     "lucide-react": "^0.525.0",
-    "next": "15.5.7",
+    "next": "15.5.9",
     "react": "^19.1.0",
     "react-dom": "^19.1.0",
     "react-responsive": "^10.0.1",