Fix VoIP audio and auto-reconnect reliability

[google-labs-jules]

This change addresses issues where VoIP calls would have no audio after a reconnection or page refresh, and where auto-reconnects (after network drop) would fail to restore the signaling channel.

Backend:

• backend/socketio_handlers.py: Added logic to handle_disconnect to detect voip_ rooms, mark the user as disconnected in the VoipCall model, and broadcast voip_user_disconnected.

Frontend:

• frontend/contexts/VoipContext.tsx:
  • Extracted peer connection creation into initializePeerConnections.
  • Updated voip_call_joined to use this new function.
  • Updated voip_my_call (used on page refresh) to call initializePeerConnections, fixing the "can't hear" issue after refresh.
  • Updated handleReconnect to emit voip_join_call instead of just voip_heartbeat, ensuring the socket is re-added to the signaling room on the server.

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PR created automatically by Jules for task 12874636545607941746 started by @8JP8

[google-labs-jules]

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