feat(ios): add online device list and pairing code redemption

- Add API methods for fetching online devices and redeeming pairing codes
- Add OnlineDevice model and corresponding ViewModel state management
- Add UI sections for online device list and pairing code input in SetupPanel
- Ensure access token is verified before connecting to signaling server

webrtc_controller_ios/web_rtc_controller_ios/ViewModel/ControllerViewModel.swift

@@ -41,6 +41,14 @@ struct ResolutionOption: Identifiable, Equatable {
     ]
 }
 
+/// 在线被控端（参考 Flutter BindingDevice.fromOnlineJson）
+struct OnlineDevice: Identifiable, Equatable {
+    let deviceId: String
+    let nickname: String
+
+    var id: String { deviceId }
+}
+
 /// 主控端 ViewModel：串联信令、WebRTC、自编码解码与 UI 状态。
 /// 所有回调均已在主线程触发，@Published 属性直接驱动 SwiftUI。
 final class ControllerViewModel: NSObject, ObservableObject {
@@ -67,6 +75,17 @@ final class ControllerViewModel: NSObject, ObservableObject {
     @Published var showAuthSheet: Bool = false
     @Published var alertMessage: String?
 
+    // MARK: - 设备发现与配对
+
+    /// 当前在线的被控端列表（GET /api/client/devices/online）。
+    @Published var onlineDevices: [OnlineDevice] = []
+    /// 是否正在加载在线设备列表。
+    @Published var isLoadingOnlineDevices: Bool = false
+    /// 配对码输入框内容。
+    @Published var pairingCode: String = ""
+    /// 是否正在兑换配对码。
+    @Published var isRedeemingPairing: Bool = false
+
     /// 是否正在录制远端视频
     @Published var isRecording: Bool = false
     /// 最近一次录制保存的文件路径（沙盒内）
@@ -156,10 +175,12 @@ final class ControllerViewModel: NSObject, ObservableObject {
             alertMessage = "请先在右上角登录账号"
             return
         }
+        loadOnlineDevices()
         showAuthSheet = true
     }
 
-    /// 鉴权弹窗确认后开始连接（已确保 accessToken 有效）。
+    /// 鉴权弹窗确认后开始连接。先确保 accessToken 有效（参考 Flutter 的 connectSignaling 先 verify/refresh），
+    /// 避免首连时直接带着过期令牌被服务端以 4001 关闭。
     func connect(authType: AuthType, authValue: String) {
         showAuthSheet = false
         pendingAuthType = authType
@@ -167,12 +188,25 @@ final class ControllerViewModel: NSObject, ObservableObject {
         isConnecting = true
         statusText = "正在连接信令服务器..."
 
-        let signaling = SignalingClient(
-            serverUrl: serverUrl.trimmingCharacters(in: .whitespaces),
-            token: accessToken)
-        signaling.delegate = self
-        signalingClient = signaling
-        signaling.connect()
+        Task {
+            do {
+                let token = try await ensureAccessToken()
+                accessToken = token
+                await MainActor.run { [weak self] in
+                    guard let self else { return }
+                    let signaling = SignalingClient(
+                        serverUrl: self.serverUrl.trimmingCharacters(in: .whitespaces),
+                        token: token)
+                    signaling.delegate = self
+                    self.signalingClient = signaling
+                    signaling.connect()
+                }
+            } catch {
+                await MainActor.run { [weak self] in
+                    self?.failConnection((error as? ApiError)?.message ?? "令牌失效，请重新登录")
+                }
+            }
+        }
     }
 
     func disconnect() {
@@ -433,6 +467,67 @@ final class ControllerViewModel: NSObject, ObservableObject {
         }
     }
 
+    /// 拉取当前在线的被控端列表（GET /api/client/devices/online，仅在线设备）。
+    /// 参考 Flutter RemoteController.loadOnlineDevices / BindingDevice.fromOnlineJson。
+    func loadOnlineDevices() {
+        guard let at = accessToken else { return }
+        isLoadingOnlineDevices = true
+        Task {
+            do {
+                let data = try await ApiClient.onlineDevices(accessToken: at)
+                let list = (data["devices"] as? [[String: Any]]) ?? []
+                let devices: [OnlineDevice] = list.compactMap { entry in
+                    guard let id = entry["deviceId"] as? String, !id.isEmpty else { return nil }
+                    let nickname = (entry["nickname"] as? String) ?? id
+                    return OnlineDevice(deviceId: id, nickname: nickname)
+                }
+                await MainActor.run { [weak self] in
+                    guard let self else { return }
+                    self.onlineDevices = devices
+                    self.isLoadingOnlineDevices = false
+                }
+            } catch {
+                await MainActor.run { [weak self] in
+                    self?.isLoadingOnlineDevices = false
+                }
+            }
+        }
+    }
+
+    /// 配对码兑换：用被控端显示的配对码建立绑定（POST /api/client/pairing/redeem）。
+    /// 参考 Flutter RemoteController.redeemPairingCode。
+    func redeemPairingCode() {
+        let code = pairingCode.trimmingCharacters(in: .whitespacesAndNewlines)
+        guard !code.isEmpty else {
+            alertMessage = "请输入配对码"
+            return
+        }
+        guard let at = accessToken else {
+            alertMessage = "请先登录账号"
+            return
+        }
+        isRedeemingPairing = true
+        Task {
+            do {
+                let data = try await ApiClient.redeemPairingCode(accessToken: at, code: code)
+                let deviceId = (data["deviceId"] as? String) ?? ""
+                let nickname = (data["nickname"] as? String) ?? deviceId
+                await MainActor.run { [weak self] in
+                    guard let self else { return }
+                    self.isRedeemingPairing = false
+                    self.pairingCode = ""
+                    self.alertMessage = "绑定成功：\(nickname)（\(deviceId)）"
+                    self.loadOnlineDevices()
+                }
+            } catch {
+                await MainActor.run { [weak self] in
+                    self?.isRedeemingPairing = false
+                    self?.alertMessage = "配对失败：\((error as? ApiError)?.message ?? error.localizedDescription)"
+                }
+            }
+        }
+    }
+
     /// 拉取 TURN 短期凭证，覆盖默认 ICE（由 WebRTCClient 读取）。
     private func loadTurnCredentials() async {
         guard let at = accessToken else { return }