fix: use WEBAPP_URL for team payment redirect instead of req.nextUrl.origin

[sean-brydon]

What does this PR do?

Fixes an issue where users get redirected to localhost:3000 after paying for a team, even when WEBAPP_URL is set to a different value.

The root cause was that the redirect after team creation was using req.nextUrl.origin (which returns the server's origin, e.g., localhost:3000 in development) instead of the configured WEBAPP_URL constant.

This change makes the redirect consistent with:

1. The onboarding redirect in the same file (line 127) which already uses WEBAPP_URL
2. The upgrade redirect in apps/web/app/api/teams/[team]/upgrade/route.ts which uses WEBAPP_URL

Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• I have updated the developer docs in /docs if this PR makes changes that would require a documentation change. N/A - no documentation changes needed.
• I confirm automated tests are in place that prove my fix is effective or that my feature works.

How should this be tested?

1. Set WEBAPP_URL in your .env to something other than http://localhost:3000 (e.g., http://app.cal.local:3000)
2. Go through the team creation flow that triggers a Stripe checkout
3. After successful payment, verify you are redirected to the URL using your configured WEBAPP_URL, not localhost:3000

Checklist

• I have read the contributing guide
• My code follows the style guidelines of this project
• I have checked if my changes generate no new warnings

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Requested by

@sean-brydon

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