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.

internal/config/livekit.go

@@ -0,0 +1,11 @@
+package config
+
+// LiveKitConfig LiveKit SFU 配置
+type LiveKitConfig struct {
+	Enabled       bool   `mapstructure:"enabled"`
+	URL           string `mapstructure:"url"`
+	APIKey        string `mapstructure:"api_key"`
+	APISecret     string `mapstructure:"api_secret"`
+	TokenTTL      int    `mapstructure:"token_ttl"`
+	WebhookSecret string `mapstructure:"webhook_secret"`
+}