channelFull was computed only in the prescreen; a second click on the channel in the room nav joined a full channel. Extract useVoiceChannelFull, use it in both places, and refuse with a "Channel full (N/N)" toast. Fixes #30 Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA