proxy.ts auth-gates every non-public path and 307-redirects to /login.
The Stripe webhook is called without a session, so it was being
redirected; Stripe does not follow redirects, so every webhook delivery
would have failed. Add /api/stripe/webhook to PUBLIC_ROUTES (scoped to
the webhook path only) and correct the route/header comments that wrongly
claimed there was no auth middleware. Caught by smoke-testing the
deployed route (POST returned 307 instead of 400).