feat: add setPlayMode SDK API with isActivated precondition

Sources/DuooomiBleSDK/DuooomiBleSDK.swift

@@ -291,6 +291,56 @@ public final class DuooomiBleSDK: NSObject {
         })
     }
 
+    /// 切换播放模式（0=单播 / 1=循环播放）。
+    ///
+    /// 复用 `BIND_DEVICE` (0x0F) 命令通道；响应类型为 `BindingResponse`。
+    /// 成功后自动刷新一次 `deviceInfo`（含最新 `loop` 字段），与 expo 端行为对齐。
+    ///
+    /// - Important: 此方法要求 **设备已和该 `userId` 完成 `bind`**（即 `isActivated == true`）。
+    ///   未绑定状态下设备会返回 `success=0`；SDK 在客户端先做守卫，直接返回失败而不发命令。
+    /// - Note: `bind` / `unbind` / `setPlayMode` 共享 `0x0F` / `0x12` opId 通道，**不能并发**。
+    public func setPlayMode(
+        _ mode: PlayMode,
+        userId: String,
+        completion: @escaping (Result<BindingResponse, Error>) -> Void
+    ) {
+        guard ensureConnected(completion: completion) else { return }
+        guard isActivated else {
+            BleLog.w("setPlayMode called before bind (isActivated=false)", "Command")
+            DispatchQueue.main.async {
+                completion(.failure(DuooomiBleError.bindingFailed("Device not bound; call bind(userId:) first")))
+            }
+            return
+        }
+        BleLog.d("Sending setPlayMode (mode=\(mode), userId=\(userId))", "Command")
+
+        sendAndWait(commandType: .bindDevice, completion: { [weak self] result in
+            guard let self = self else { return }
+            switch result {
+            case .failure(let error):
+                completion(.failure(error))
+            case .success(let data):
+                do {
+                    let resp = try self.decodeResponse(BindingResponse.self, from: data)
+                    if resp.success != 1 {
+                        BleLog.w("setPlayMode failed: device rejected", "Command")
+                        completion(.failure(DuooomiBleError.bindingFailed("Set play mode failed")))
+                        return
+                    }
+                    BleLog.i("setPlayMode success: mode=\(mode)", "Command")
+                    // 自动刷新 deviceInfo（含最新 loop 字段）
+                    self.getDeviceInfo { _ in
+                        completion(.success(resp))
+                    }
+                } catch {
+                    completion(.failure(error))
+                }
+            }
+        }, send: {
+            try self.deviceInfoService.setPlayMode(userId: userId, loop: mode)
+        })
+    }
+
     /// 解除设备绑定
     public func unbind(userId: String, completion: @escaping (Result<UnbindResponse, Error>) -> Void) {
         guard ensureConnected(completion: completion) else { return }