feat(webrtc): 添加公共ICE服务器支持和优化HID延迟

- 重构ICE配置：将TURN配置改为统一的ICE配置，支持STUN和多TURN URL
- 添加公共ICE服务器：类似RustDesk，用户留空时使用编译时配置的公共服务器
- 优化DataChannel HID消息：使用tokio::spawn立即处理，避免依赖webrtc-rs轮询
- 添加WebRTCReady事件：客户端等待此事件后再建立连接
- 初始化时启动音频流，确保WebRTC可订阅
- 移除多余的trace/debug日志减少开销
- 更新前端配置界面支持公共ICE服务器显示

src/events/types.rs

@@ -187,6 +187,18 @@ pub enum SystemEvent {
         device: String,
     },
 
+    /// WebRTC is ready to accept connections
+    ///
+    /// Sent after video frame source is connected to WebRTC pipeline.
+    /// Clients should wait for this event before attempting to create WebRTC sessions.
+    #[serde(rename = "stream.webrtc_ready")]
+    WebRTCReady {
+        /// Current video codec
+        codec: String,
+        /// Whether hardware encoding is being used
+        hardware: bool,
+    },
+
     /// Stream statistics update (sent periodically for client stats)
     #[serde(rename = "stream.stats_update")]
     StreamStatsUpdate {
@@ -485,6 +497,7 @@ impl SystemEvent {
             Self::StreamDeviceLost { .. } => "stream.device_lost",
             Self::StreamReconnecting { .. } => "stream.reconnecting",
             Self::StreamRecovered { .. } => "stream.recovered",
+            Self::WebRTCReady { .. } => "stream.webrtc_ready",
             Self::StreamStatsUpdate { .. } => "stream.stats_update",
             Self::StreamModeChanged { .. } => "stream.mode_changed",
             Self::HidStateChanged { .. } => "hid.state_changed",