Livekit Egress Webhook

Receive LiveKit egress lifecycle events and reflect them onto the corresponding session row.

LiveKit's webhooks carry a signed JWT in the Authorization header. The WebhookReceiver from livekit.api verifies it against our api secret and parses the body — never trust the payload before that runs.

Events we handle:

• egress_started → status='active'
• egress_updated → status='active' (no-op if already active)
• egress_ended → status='completed' on EGRESS_COMPLETE, status='failed' on EGRESS_FAILED/ABORTED

Unknown events are 200-OK'd silently — LiveKit retries on non-2xx and we don't want to enter a retry loop over an event we don't model yet.