Voice calling (1‑on‑1)

[mrsumanbiswas]

Implement one‑on‑one voice calls using WebRTC.

• Set up a signaling server (or reuse the existing WebSocket) for call initiation, acceptance, and ICE candidate exchange
• Flutter client: use a WebRTC plugin (flutter_webrtc)
• UI: call screen with speaker/mute buttons, call timer, hang‑up
• Handle call state: ringing, answered, ended, missed
• Integrate with push notifications (for incoming calls when app is in background)

Aim for a reliable and low‑latency call experience.