Customer self-service billing portal is accessible

Without a self-service billing portal, every payment-method update, card expiration, and address change becomes a support ticket — and a meaningful percentage of involuntary churn comes from expired cards that users would have replaced themselves if given the option. Enterprise buyers specifically screen for self-service billing during procurement because their finance teams refuse to route routine card updates through a vendor's support queue.

Wire up Stripe Customer Portal and surface a Manage Billing button in account settings. Create app/api/billing/portal/route.ts that calls stripe.billingPortal.sessions.create({ customer: user.stripe_customer_id, return_url }) and redirects to session.url. Configure the portal features in the Stripe Dashboard under Settings → Billing → Customer portal.