feat(webrtc): integrate Cloudflare TURN/STUN servers

- Add backend endpoint to fetch ICE server credentials from Cloudflare
- Implement dynamic ICE server configuration in frontend
- Add fallback to public STUN servers when Cloudflare unavailable
- Create comprehensive test suite for WebRTC API endpoint
- Update environment configuration with Cloudflare TURN credentials

Backend changes:
- New route: GET /api/webrtc/ice-servers (authenticated)
- Fetches temporary credentials from Cloudflare API with 24h TTL
- Returns formatted ICE servers for RTCPeerConnection
- Graceful fallback to Google STUN servers on errors

Frontend changes:
- Remove hardcoded ICE servers from useWebRTC hook
- Fetch ICE servers dynamically from backend on mount
- Store servers in ref for peer connection initialization
- Add webrtcAPI service for backend communication

Tests:
- 9 comprehensive tests covering all scenarios
- 100% coverage for webrtc.js route
- Tests authentication, success, and all fallback scenarios

backend/.env.development.example

@@ -62,3 +62,8 @@ MATCHING_MIN_INTERVAL_SEC=60
 # Cloudflare Turnstile (CAPTCHA)
 # Get your secret key from: https://dash.cloudflare.com/
 TURNSTILE_SECRET_KEY=your-secret-key-here
+
+# Cloudflare TURN/STUN
+# Get your credentials from: https://dash.cloudflare.com/ -> Calls -> TURN
+CLOUDFLARE_TURN_TOKEN_ID=your-turn-token-id-here
+CLOUDFLARE_TURN_API_TOKEN=your-turn-api-token-here