Bump next from 14.2.35 to 15.5.14 in /site

Bumps [next](https://github.com/vercel/next.js) from 14.2.35 to 15.5.14.
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](vercel/next.js@v14.2.35...v15.5.14)

---
updated-dependencies:
- dependency-name: next
  dependency-version: 15.5.14
  dependency-type: direct:production
...

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Author: dependabot[bot]