JWT-based authenticated event processing #6232

Summary

Add JWT-based authentication for event processing. This enables authenticated requests to the event system, particularly important for the HTTP endpoint model where events are invoked without a websocket session.

Why

With event handlers exposed as HTTP POST endpoints (1f), there needs to be a standard authentication mechanism for server-to-server calls, agent integrations, and webhook consumers that don't have a websocket connection or browser session.

Part of the Reflex Framework Roadmap — Section 1m.