feat(call): integrate LiveKit for voice and video calling

Replace the manual WebRTC signaling implementation with LiveKit SFU. This includes:
- Adding LiveKit service, handler, and configuration.
- Updating Docker Compose to include LiveKit server, Redis, and PostgreSQL.
- Refactoring `CallService` and `WSHandler` to support LiveKit room readiness instead of raw SDP/ICE relaying.
- Adding new API endpoints for LiveKit token generation and webhooks.
- Removing deprecated WebRTC configuration and manual signaling DTOs.

configs/livekit.yaml

@@ -0,0 +1,32 @@
+# LiveKit Server Configuration
+# See https://docs.livekit.io/realtime/server/config/ for all options
+
+port: 7880
+rtc:
+  tcp_port: 7881
+  udp_port: 7882
+  use_external_ip: false
+  # Enable TURN/TLS relay for restrictive networks
+  port_range_start: 7881
+  port_range_end: 7882
+  node_ip: 127.0.0.1
+
+keys:
+  devkey: u1sLYiHWe4HIr3KrJrvknIleoHdgHdDqSjfkBvRs2AlA
+
+logging:
+  level: info
+
+# Redis for distributed state (required)
+redis:
+  address: livekit-redis:6379
+
+# PostgreSQL for persistent storage (rooms, participants, egress)
+db:
+  address: postgres://postgres:postgres@livekit-postgres:5432/livekit?sslmode=disable
+
+# Webhook for call history persistence
+# webhook:
+#   urls:
+#     - http://app:8080/api/v1/calls/webhook
+#   api_key: devkey