Drop the global _APP_NOTIFICATIONS_WEBHOOK_SECRET env var. There's no
analogous global webhook secret in Appwrite; the existing Webhooks
worker carries a per-webhook signatureKey on the webhook document.
Move the same pattern into the Notification event: each webhook
recipient may carry an optional signatureKey, which the worker
forwards to the Webhook adapter for HMAC-SHA256 signing. Recipients
without a key are delivered unsigned and a tag is logged for audit.
Jake Barnby
7839b3bb3f