Function send_webhook 

pub fn send_webhook(
    event_type: WebhookEventType,
    task_id: &str,
    task_title: &str,
    previous_status: Option<&str>,
    current_status: Option<&str>,
    note: Option<&str>,
    config: &WebhookConfig,
    timestamp_rfc3339: &str,
)

Send a webhook notification (non-blocking, enqueues for delivery).

This function returns immediately after enqueueing the webhook. Delivery happens asynchronously in a background worker thread.