Implement answer polling for offerer side

Host now polls for answered offers every 2 seconds using the new
efficient batch endpoint. When an answer is received, the host
automatically sets the remote description to complete the WebRTC
connection.

Changes:
- Store offerId to RTCPeerConnection mapping when publishing
- Poll for answered offers with timestamp filtering
- Automatically handle incoming answers
- Track last answer timestamp to avoid reprocessing

This completes the bidirectional WebRTC signaling flow.

package-lock.json

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