feat: add query param webhook auth and fix empty body parsing

[scolastico]

This PR introduces a new Query webhook authentication style and resolves an issue with empty webhook payloads.

Changes:

• Query Webhook Authentication: Added a new webhook integration (QueryAuth) that allows external services to authenticate using a ?secret=... query parameter instead of HTTP headers. It also optionally supports extracting the target branch via a ?branch=... parameter (defaults to main).
• Listener Infrastructure Updates: Updated the VerifySecret and ExtractBranch traits across the router to receive the parsed query map, passing it down to all webhook handlers.
• Empty Body Fix: Fixed a bug where Action webhooks would fail with an EOF while parsing a value error if triggered with an empty request body. It now safely defaults to a Null JSON value when the body is empty.
• UI Enhancements: Added the new Query auth style to the UI dropdown options. When selected, the UI now displays helpful usage text underneath the Webhook URL field explaining the required secret and optional branch parameters.