docs: add missing doc comments and fix copy-paste error in Room.swift

[Sleywill]

Summary

Two types of fix in Room.swift:

1. Copy-paste error (bug)

serverNodeId had the same doc comment as serverRegion:

// Before (wrong — copy-pasted from serverRegion)
/// Region code the client is currently connected to.
public var serverNodeId: String? { _state.serverInfo?.nodeID.nilIfEmpty }

// After (correct)
/// The ID of the server node the client is currently connected to.
public var serverNodeId: String? { _state.serverInfo?.nodeID.nilIfEmpty }

2. Missing doc comments

Added /// documentation to 10 public properties that had none:

name, serverVersion, remoteParticipants, activeSpeakers, creationTime, maxParticipants, participantCount, publishersCount, token, disconnectError

No behaviour changes.

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[pblazej]

@Sleywill could you sign the cla?