Unified LiveKitAPI exposes all server endpoints

Minor Changes

• Add LiveKitAPI, a unified entry point that exposes every server API through a property (api.room, api.egress, api.ingress, api.sip, api.agentDispatch, api.connector). It can be constructed with an API key and secret, or with a pre-signed token (no secret required, so it can run client-side), and falls back to the LIVEKIT_URL, LIVEKIT_API_KEY, LIVEKIT_API_SECRET, and LIVEKIT_TOKEN environment variables. Individual clients also accept a token via ClientOptions. - #695 (@davidzhao)

• Add SipCallError, a TwirpError subclass thrown by SipClient.createSipParticipant / transferSipParticipant when a call fails with a SIP status. It exposes the SIP response code and reason as sipStatusCode / sipStatus getters, while other error metadata remains available via metadata. - #695 (@davidzhao)

Patch Changes

• feat: auto failover APIs with LK Cloud - #686 (@davidzhao)