docs(examples): align WorkOS README redirect URI with callback route

[LadyBluenotes]

Goal

Make the WorkOS example setup instructions use the callback URL implemented by the current AuthKit example.

Scope

• Update examples/react/start-workos/README.md so WORKOS_REDIRECT_URI uses http://localhost:3000/api/auth/callback.
• Keep the README, .env.example, WorkOS dashboard setup instruction, and registered callback route aligned.
• Confirm the example builds after the documentation update.

Related Work

This follows the callback-route corrections in #4534 and #5048:

• examples: fix workos example callback path #4534
• fix: workos router.tsx typo + move api route into api/auth/callback.tsx #5048
• fix(example): work-os api callback to reflect documentation #4900

[soheilnikroo]

@LadyBluenotes, I updated examples/react/start-workos/README.md so the WORKOS_REDIRECT_URI env example uses http://localhost:3000/api/auth/callback, matching .env.example, the WorkOS dashboard setup step, and the registered callback route at /api/auth/callback. Verified the example builds successfully.