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/Signaling/SignalingClient.swift

@@ -19,6 +19,10 @@ final class SignalingClient: NSObject {
     private var session: URLSession?
     private var task: URLSessionWebSocketTask?
     private var manuallyClosed = false
+    /// WebSocket 握手是否已完成（didOpen 后置为 true）
+    private var isOpened = false
+    /// 是否已上报过断开/失败，避免重复回调
+    private var didNotifyClosure = false
 
     init(serverUrl: String, deviceId: String) {
         self.serverUrl = serverUrl
@@ -32,16 +36,20 @@ final class SignalingClient: NSObject {
             return
         }
         manuallyClosed = false
+        isOpened = false
+        didNotifyClosure = false
         let config = URLSessionConfiguration.default
         config.timeoutIntervalForRequest = 15
         session = URLSession(configuration: config, delegate: self, delegateQueue: nil)
         task = session?.webSocketTask(with: url)
+        // 接收循环在 didOpenWithProtocol（握手完成）后再启动，
+        // 避免在 socket 未真正连接时调用 receive 触发 Code 57。
         task?.resume()
-        receiveLoop()
     }
 
     func disconnect() {
         manuallyClosed = true
+        isOpened = false
         task?.cancel(with: .normalClosure, reason: "Disconnecting".data(using: .utf8))
         task = nil
         session?.invalidateAndCancel()
@@ -85,9 +93,31 @@ final class SignalingClient: NSObject {
                 }
                 self.receiveLoop()
             case .failure(let error):
-                if !self.manuallyClosed {
-                    self.notifyError(error.localizedDescription)
-                }
+                self.handleReceiveFailure(error)
+            }
+        }
+    }
+
+    /// 处理接收失败：区分"正常断开"与"连接失败"。
+    /// Socket 已断开（Code 57 等）视为断开而非致命错误。
+    private func handleReceiveFailure(_ error: Error) {
+        guard !manuallyClosed, !didNotifyClosure else { return }
+        didNotifyClosure = true
+
+        let nsError = error as NSError
+        // NSPOSIXErrorDomain Code 57: Socket is not connected（连接已断开）
+        let isDisconnect = (nsError.domain == NSPOSIXErrorDomain && nsError.code == 57)
+            || (nsError.domain == NSURLErrorDomain
+                && (nsError.code == NSURLErrorNetworkConnectionLost
+                    || nsError.code == NSURLErrorCancelled))
+
+        DispatchQueue.main.async {
+            if self.isOpened || isDisconnect {
+                // 连接已建立过后再断开，按"断开"处理
+                self.delegate?.signalingDidDisconnect()
+            } else {
+                // 从未成功建立连接，按"连接失败"处理
+                self.delegate?.signaling(didFail: error.localizedDescription)
             }
         }
     }
@@ -106,6 +136,9 @@ extension SignalingClient: URLSessionWebSocketDelegate {
     func urlSession(_ session: URLSession,
                     webSocketTask: URLSessionWebSocketTask,
                     didOpenWithProtocol protocol: String?) {
+        isOpened = true
+        // 握手完成后再启动接收循环，避免 socket 未连接时 receive 报错
+        receiveLoop()
         registerDevice()
         DispatchQueue.main.async {
             self.delegate?.signalingDidConnect()
@@ -116,7 +149,9 @@ extension SignalingClient: URLSessionWebSocketDelegate {
                     webSocketTask: URLSessionWebSocketTask,
                     didCloseWith closeCode: URLSessionWebSocketTask.CloseCode,
                     reason: Data?) {
-        guard !manuallyClosed else { return }
+        isOpened = false
+        guard !manuallyClosed, !didNotifyClosure else { return }
+        didNotifyClosure = true
         DispatchQueue.main.async {
             self.delegate?.signalingDidDisconnect()
         }