Test webhook delivery

Send a synthetic test event to a specific webhook endpoint.

Use this endpoint to validate receiver reachability, authentication/signature handling, and payload processing before relying on live events.

Response behavior:

• On success, returns statusCode 200.
• On delivery failure, returns the failure statusCode and a Base64-encoded HAR payload in 'har' for deep diagnostics.

Recommended usage:

1. Create or update webhook configuration.
2. Run this test endpoint.
3. If it fails, decode the HAR payload and inspect request/response details.
4. Re-test after receiver-side fixes until statusCode is 200.

This endpoint is intended for validation and troubleshooting, not production event simulation at scale.