MoqRelayStateChanged

Lifecycle state of a single upstream MoQT relay an egest is publishing to. The relay_url is included on every event so a client SDK can correlate events when there are multiple configured relays.

Sequence (per relay):

CONNECTING → ANNOUNCING → CONNECTED → READY ↓ (on retry) ANNOUNCE_FAILED { reason, retry_ms } → loop back to ANNOUNCING

At any time after CONNECTING: DISCONNECTED { reason }

CONNECTED and READY are deliberately separate so a UI can distinguish "we have a session, but the namespace hasn’t been accepted yet" from "the relay is publishing-ready".