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/Utils/ApiClient.swift

@@ -45,12 +45,32 @@ struct ApiClient {
         return try await get("/api/client/turn-credentials", accessToken: accessToken)
     }
 
+    /// 在线被控端列表（仅当前在线、本账号可连接的设备）。
+    /// 参考 Flutter `devices_online`（GET /api/client/devices/online）。
+    static func onlineDevices(accessToken: String) async throws -> [String: Any] {
+        return try await get("/api/client/devices/online", accessToken: accessToken)
+    }
+
+    /// 配对码兑换：用被控端显示的配对码建立绑定。
+    /// 参考 Flutter `redeemPairingCode`（POST /api/client/pairing/redeem）。
+    static func redeemPairingCode(accessToken: String, code: String) async throws -> [String: Any] {
+        let body: [String: Any] = ["code": code]
+        return try await post("/api/client/pairing/redeem", body: body, accessToken: accessToken)
+    }
+
     // MARK: - Private
 
     private static func post(_ path: String, body: [String: Any]) async throws -> [String: Any] {
+        return try await post(path, body: body, accessToken: nil)
+    }
+
+    private static func post(_ path: String, body: [String: Any], accessToken: String?) async throws -> [String: Any] {
         var req = URLRequest(url: URL(string: baseURL + path)!)
         req.httpMethod = "POST"
         req.setValue("application/json", forHTTPHeaderField: "Content-Type")
+        if let accessToken, !accessToken.isEmpty {
+            req.setValue("Bearer \(accessToken)", forHTTPHeaderField: "Authorization")
+        }
         req.httpBody = try JSONSerialization.data(withJSONObject: body)
         return try await perform(req)
     }