fix: use route to handle callback in next server actions

[wangsijie]

Summary

In Next.js server actions sample:

Use route handler to handle sign in callback, the prev page handler can not get search params in Vercel, because it is a client component.

Testing

Tested in Vercel.

Checklist

• [ ] .changeset
• [ ] unit tests
• [ ] integration tests
• [ ] necessary TSDoc comments