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/Views/SetupPanelView.swift

@@ -26,6 +26,63 @@ struct SetupPanelView: View {
                     TextField("目标设备 ID", text: $viewModel.targetDeviceId)
                         .autocapitalization(.allCharacters)
                         .disableAutocorrection(true)
+
+                    Button {
+                        viewModel.loadOnlineDevices()
+                    } label: {
+                        HStack {
+                            Text("刷新在线设备")
+                            Spacer()
+                            if viewModel.isLoadingOnlineDevices {
+                                ProgressView()
+                            }
+                        }
+                    }
+                }
+
+                if !viewModel.onlineDevices.isEmpty {
+                    Section("在线设备（点击填入目标 ID）") {
+                        ForEach(viewModel.onlineDevices) { device in
+                            Button {
+                                viewModel.targetDeviceId = device.deviceId
+                            } label: {
+                                HStack {
+                                    VStack(alignment: .leading, spacing: 2) {
+                                        Text(device.nickname)
+                                        Text(device.deviceId)
+                                            .font(.system(.caption, design: .monospaced))
+                                            .foregroundColor(.secondary)
+                                    }
+                                    Spacer()
+                                    if viewModel.targetDeviceId == device.deviceId {
+                                        Image(systemName: "checkmark")
+                                            .foregroundColor(.accentColor)
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+
+                Section("配对码兑换（建立新绑定）") {
+                    HStack {
+                        TextField("输入被控端显示的配对码", text: $viewModel.pairingCode)
+                            .textInputAutocapitalization(.never)
+                            .autocorrectionDisabled()
+                        Button {
+                            viewModel.redeemPairingCode()
+                        } label: {
+                            if viewModel.isRedeemingPairing {
+                                ProgressView()
+                            } else {
+                                Text("兑换")
+                            }
+                        }
+                        .disabled(viewModel.isRedeemingPairing || viewModel.pairingCode.trimmingCharacters(in: .whitespaces).isEmpty)
+                    }
+                    Text("在被控端生成配对码后填入此处即可建立绑定，绑定成功后会出现在上方在线设备列表中。")
+                        .font(.caption)
+                        .foregroundColor(.secondary)
                 }
 
                 Section {