build(deps): bump next from 15.4.7 to 15.4.8 in /playground/frontend (#1026)

Bumps [next](https://github.com/vercel/next.js) from 15.4.7 to 15.4.8.
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](vercel/next.js@v15.4.7...v15.4.8)

---
updated-dependencies:
- dependency-name: next
  dependency-version: 15.4.8
  dependency-type: direct:production
...

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Author: dependabot[bot]