Conditional delete for webhooks (delete only if unchanged since read)

Summary DELETE /v1/webhooks/:webhookId deletes unconditionally. A client that decides to delete a webhook based on what it read earlier cannot make the delete depend on that read, so a concurrent update between the read and the delete is lost. Please add an optional precondition so the delete only happens if the webhook is unchanged since the client read it. Use case The Appwrite MCP server ([appwrite/mcp#127]( implements MCP Events by managing one Appwrite webhook per subscription in the user's project. The server is stateless: the webhook is the only record of the subscription, and its name carries the lease expiry. On each events/subscribe, the server cleans up the caller's webhooks whose lease expired more than 10 minutes ago, so stale subscriptions don't hold Free-plan webhook slots. Cleanup lists the webhooks, re-reads each candidate, and deletes it if its name and $updatedAt are unchanged. The window between that re-read and the DELETE can't be closed f…