PixelProof v1.1.0: Revenue mechanics — webhook idempotency, Rewardful, and kill-trigger monitoring

This release closed the gap between "checkout works" and "checkout works safely at scale." Stripe webhooks now write to a `subscription_events` ledger with idempotency checks, so a retried webhook delivery can't double-process a payment. Seven kill-trigger SQL views started watching for the failure patterns most likely to blow up a subscription business quietly — refund spikes, failed-payment clusters, and similar.

The Vercel environment batch that went out this day also activated Rewardful affiliate tracking and an automatic Section 32-style plan upgrade path. On the observability side, Sentry and PostHog wiring, a Session Replay Verifier harness, and four new end-to-end assertions gave the M2 milestone a real safety net instead of relying on manual spot checks.