build(deps): bump next and react-email in /react-email-preview

Bumps [next](https://github.com/vercel/next.js) to 15.0.4 and updates ancestor dependency [react-email](https://github.com/resend/react-email/tree/HEAD/packages/react-email). These dependencies need to be updated together.


Updates `next` from 14.2.10 to 15.0.4
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](vercel/next.js@v14.2.10...v15.0.4)

Updates `react-email` from 3.0.2 to 3.0.4
- [Release notes](https://github.com/resend/react-email/releases)
- [Changelog](https://github.com/resend/react-email/blob/canary/packages/react-email/CHANGELOG.md)
- [Commits](https://github.com/resend/react-email/commits/[email protected]/packages/react-email)

---
updated-dependencies:
- dependency-name: next
  dependency-type: indirect
- dependency-name: react-email
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>