Add voice channel functionality with WebRTC peer-to-peer audio:
- Add VoiceSignalingConsumer for WebRTC signaling and peer coordination
- Add GlobalConsumer for real-time presence and voice status updates
- Add voice channel type to Channel model with current_voice_channel tracking on UserProfile
- Add voice controls UI (mute, deafen, disconnect) in status panel
- Add voice member list display in sidebar with avatar support
- Add
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