Stripe Webhook

Handle Stripe webhook events.

Currently handled:

• customer.subscription.created
• customer.subscription.updated
• customer.subscription.deleted
• customer.subscription.pending_update_applied
• customer.subscription.pending_update_expired
• account.updated (Stripe Connect Express — mirrors a seller's charges_enabled / payouts_enabled capability flags onto the User)
• checkout.session.completed (F-01 Increment 2 — marketplace destination charge confirmed: mint the hired clone, flip the purchase AWAITING_PAYMENT → COMPLETED, record realized revenue, fire playbook_hired)
• checkout.session.expired / .async_payment_failed (flip AWAITING_PAYMENT → FAILED so the buyer can retry; no clone)

Returns:

• 200 with {"status": "ok", "event_type": ..., "deduplicated": false} on first-time processing.
• 200 with {"status": "ok", "deduplicated": true} on a replay (so Stripe stops retrying).
• 400 on signature failure / malformed payload / malformed signature header (no body, missing header, expired timestamp, bad HMAC).
• 503 with detail "Stripe not configured" when the env secret is unset (matched by the Sentry allowlist — see rule #7).