[extensions] Declare optional React type peer for next-themes

[sharmila-oai]

What's the problem this PR addresses?

next-themes publishes declarations that reference React types without declaring an @types/react peer. Yarn already infers optional type peers; this entry records the missing declaration for other consumers of the shared extensions database, including pnpm.

How did you fix it?

Add an optional @types/react peer for next-themes@>=0.2.1 <=0.4.6. The matching package-author draft fixes the manifest for future releases.

Verification with unmodified pnpm 11.19.0 and its global virtual store:

• Applying this entry restores ThemeProvider prop checking in 0.2.1 and setTheme callback typing in 0.4.6.
• The corrected 0.4.6 consumer passes a frozen offline reinstall and typecheck without changing its lockfile.

Yarn's six existing package-extension acceptance tests, focused ESLint, and yarn version check pass.

Checklist

• I have read the Contributing Guide.
• I have set the packages that need to be released for my changes to be effective.
• I will check that all automated PR checks pass before the PR gets reviewed.

[sharmila-oai]

@arcanis could you take a look?