feat(TRA-372): live groupcall backend — WebRTC signaling + session control
- Add Django Channels 4 + channels-redis to requirements and INSTALLED_APPS
- Upgrade ASGI config to ProtocolTypeRouter with JWT-authenticated WebSocket routing
- Add JWTAuthMiddleware for WebSocket token auth via query param
- Add CallSession, CallParticipant, CallEvent models with migration 0004
- MeetingCallConsumer: join/leave, P2P SDP/ICE relay via per-user groups,
instructor mute/unmute/kick with DB audit and WS broadcast
- REST endpoints: GET/POST/DELETE /meetings/{id}/call/ (session lifecycle),
POST /moderate/ (mute/unmute/kick), POST /screen-share/, GET /events/ (audit log)
- IsMeetingModerator permission (accepts training:signoff or meeting:moderate)
- Services: get_or_create_call_session, end_call_session, apply_moderation_action,
toggle_screen_share with full CallEvent audit trail
- Integration tests covering REST lifecycle, moderation, and WebSocket signaling
Co-Authored-By: Paperclip <noreply@paperclip.ing>
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