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/config.go

@@ -27,7 +27,7 @@ type Config struct {
 	Casbin            CasbinConfig            `mapstructure:"casbin"`
 	Encryption        EncryptionConfig        `mapstructure:"encryption"`
 	HotRank           HotRankConfig           `mapstructure:"hot_rank"`
-	WebRTC            WebRTCConfig            `mapstructure:"webrtc"`
+	LiveKit           LiveKitConfig           `mapstructure:"livekit"`
 	Report            ReportConfig            `mapstructure:"report"`
 	Sensitive         SensitiveConfig         `mapstructure:"sensitive"`
 	JPush             JPushConfig             `mapstructure:"jpush"`
@@ -168,10 +168,6 @@ func Load(configPath string) (*Config, error) {
 	viper.SetDefault("hot_rank.recent_window_hours", 168)
 	viper.SetDefault("hot_rank.recent_fetch_limit", 500)
 	viper.SetDefault("hot_rank.candidate_cap", 800)
-	// WebRTC 默认值（Google 公共 STUN 服务器）
-	viper.SetDefault("webrtc.ice_servers", []map[string]any{
-		{"urls": []string{"stun:stun.l.google.com:19302"}},
-	})
 	// Report 默认值
 	viper.SetDefault("report.auto_hide_threshold", 3)
 	viper.SetDefault("jpush.enabled", false)
@@ -213,6 +209,13 @@ func Load(configPath string) (*Config, error) {
 	viper.SetDefault("push_worker.max_retries", 3)
 	viper.SetDefault("push_worker.max_stream_len", 100000)
 	viper.SetDefault("push_worker.idle_timeout_ms", 30000)
+	// LiveKit 默认值
+	viper.SetDefault("livekit.enabled", false)
+	viper.SetDefault("livekit.url", "http://localhost:7880")
+	viper.SetDefault("livekit.api_key", "devkey")
+	viper.SetDefault("livekit.api_secret", "")
+	viper.SetDefault("livekit.token_ttl", 600)
+	viper.SetDefault("livekit.webhook_secret", "")
 
 	if err := viper.ReadInConfig(); err != nil {
 		return nil, fmt.Errorf("failed to read config: %w", err)