Missing information on Realtime participant token expiration

### Existing documentation URL(s)

https://developers.cloudflare.com/realtime/realtimekit/concepts/participant/#participant-tokens

### What changes are you suggesting?

The docs state that participant tokens expire, but doesn't say **how it's reflected in the API**. API field? Error response? Something else?

Please clarify how a developer can find out a token has expired.

### Additional information

_No response_