build(deps): bump next from 16.2.7 to 16.3.1 in /frontend

Bumps [next](https://github.com/vercel/next.js) from 16.2.7 to 16.3.1.
- [Release notes](https://github.com/vercel/next.js/releases)
- [Commits](vercel/next.js@v16.2.7...v16.3.1)

---
updated-dependencies:
- dependency-name: next
  dependency-version: 16.3.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

frontend/package.json

@@ -50,7 +50,7 @@
     "geist": "^1.7.2",
     "input-otp": "^1.4.1",
     "lucide-react": "^1.17.0",
-    "next": "^16.2.7",
+    "next": "^16.3.1",
     "next-themes": "^0.4.6",
     "react": "^19.2.8",
     "react-day-picker": "^10.0.1",