fix(react-email): broken paths on email build output for Windows

[TyMick]

Fixes #2420.

@MrMaxie's intuition was right on—replacing backslashes with forward slashes in absolute paths in the next.config.js template fixes Windows builds on my end.

Before this change, if I run the following on Windows:

pnpm create email
cd react-email-starter
pnpm i
pnpm build

it fails during the Next.js build, citing a very mangled version of the project path in the error message.

After this change, if I Yalc my local react-email package into my react-email-starter project, the build succeeds!

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Summary by cubic

Normalizes Windows paths in the generated Next.js config to fix build failures on Windows. Replaces backslashes with forward slashes in absolute paths used during react-email builds.

• Bug Fixes
  • Convert backslashes in process.cwd() and builtPreviewAppPath before writing next.config.js.
  • Prevents mangled path errors during Next.js build on Windows (react-email-starter).

[changeset-bot]

🦋 Changeset detected

Latest commit: 8808122

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
react-email	Patch
@react-email/preview-server	Patch

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[pkg-pr-new]

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npm i https://pkg.pr.new/resend/react-email@2475

commit: 8808122

[cubic-dev-ai]

No issues found across 1 file

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[gabrielmfern]

Amazing work, thank you very much for this!