The payment webhook drops about 3% of Stripe events because delivery retries are disabled, so paid subscriptions silently fail to activate and we lose revenue every day this runs. Enabling exponential-backoff retries in `webhook.yaml` and persisting each event id makes delivery idempotent and closes the gap. @miguel is on-call for billing and must merge and deploy this before the month-end invoicing run, otherwise the reconciliation report is wrong again and finance has to patch it by hand.
