The limit was checked against participants LiveKit already had, so
tokens issued but not yet connected were not counted: two users
pressing Join together could both get into a 1-person channel.
Serialise the check per room and give each admitted user a 30 s
reservation, counted like a present user until LiveKit lists them or
it expires.
Refs #25
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5