feat(ios): 添加远端视频录制功能并优化信令连接稳定性

- 新增 VideoRecorder 组件，支持 WebRTC 和自编码两种模式录制远端视频为 MP4
- 优化 SignalingClient 连接管理，修复 WebSocket 握手前 receive 导致的断开问题
- 重构控制面板 UI，支持统计信息折叠展开和录制控制按钮
- 添加录制状态指示、保存路径提示及断开自动取消录制逻辑
- 更新项目配置和文档，补充录制功能说明

webrtc_controller_ios/web_rtc_controller_ios/WebRTC/WebRTCClient.swift

@@ -46,6 +46,8 @@ final class WebRTCClient: NSObject {
     private var videoChannel: RTCDataChannel?
     private weak var remoteRenderer: RTCVideoRenderer?
     private var remoteVideoTrack: RTCVideoTrack?
+    /// 额外的渲染器（用于把远端视频帧 fan-out 给录制器，WebRTC 模式）
+    weak var extraRenderer: RTCVideoRenderer?
     private var connected = false
 
     init(signaling: SignalingClient, myDeviceId: String) {
@@ -208,6 +210,9 @@ final class WebRTCClient: NSObject {
         if let track = remoteVideoTrack, let renderer = remoteRenderer {
             track.remove(renderer)
         }
+        if let track = remoteVideoTrack, let extra = extraRenderer {
+            track.remove(extra)
+        }
         remoteVideoTrack = nil
         peerConnection?.close()
         peerConnection = nil
@@ -289,6 +294,9 @@ extension WebRTCClient: RTCPeerConnectionDelegate {
             if let renderer = self.remoteRenderer {
                 track.add(renderer)
             }
+            if let extra = self.extraRenderer {
+                track.add(extra)
+            }
         }
     }
 }