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）