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/config.yaml

@@ -333,3 +333,15 @@ version_log:
   enabled: false             # 启用后客户端可使用 /conversations/sync 增量同步
   sync_limit: 100            # 单次同步最大返回变更条数
   max_sync_gap: 1000         # 版本差距超过此值建议全量同步
+
+# LiveKit SFU 配置（语音/视频通话）
+# 环境变量:
+#   APP_LIVEKIT_ENABLED, APP_LIVEKIT_URL, APP_LIVEKIT_API_KEY, APP_LIVEKIT_API_SECRET
+#   APP_LIVEKIT_TOKEN_TTL, APP_LIVEKIT_WEBHOOK_SECRET
+livekit:
+  enabled: false
+  url: "http://localhost:7880"
+  api_key: "devkey"
+  api_secret: "u1sLYiHWe4HIr3KrJrvknIleoHdgHdDqSjfkBvRs2AlA"
+  token_ttl: 600          # token 有效期（秒）
+  webhook_secret: ""      # webhook 签名密钥（与 LiveKit 服务端配置一致）

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