feat: extend BindPayload with optional loop field; add setPlayMode service

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Sources/DuooomiBleSDK/Services/DeviceInfoService.swift

@@ -27,14 +27,26 @@ final class DeviceInfoService {
     func bindDevice(userId: String) throws {
         try protocolService.sendJSON(
             type: .bindDevice,
-            payload: BindPayload(type: CommandType.bindDevice.rawValue, userId: userId)
+            payload: BindPayload(type: CommandType.bindDevice.rawValue, userId: userId, loop: nil)
         )
     }
 
     func unbindDevice(userId: String) throws {
         try protocolService.sendJSON(
             type: .unbindDevice,
-            payload: BindPayload(type: CommandType.unbindDevice.rawValue, userId: userId)
+            payload: BindPayload(type: CommandType.unbindDevice.rawValue, userId: userId, loop: nil)
+        )
+    }
+
+    /// 切换播放模式（复用 BIND_DEVICE 命令字 0x0F，payload 携带 loop 字段）
+    func setPlayMode(userId: String, loop: PlayMode) throws {
+        try protocolService.sendJSON(
+            type: .bindDevice,
+            payload: BindPayload(
+                type: CommandType.bindDevice.rawValue,
+                userId: userId,
+                loop: UInt8(loop.rawValue)
+            )
         )
     }
 
@@ -63,9 +75,25 @@ private struct CommandPayload: Encodable {
     let type: UInt8
 }
 
-private struct BindPayload: Encodable {
+/// 绑定 / 解绑 / 切模式 共用 payload。
+/// `loop == nil` 时严格省略该字段（不写 null），与 Expo 端 zod.optional 行为对齐。
+struct BindPayload: Encodable {
     let type: UInt8
     let userId: String
+    let loop: UInt8?
+
+    enum CodingKeys: String, CodingKey {
+        case type, userId, loop
+    }
+
+    func encode(to encoder: Encoder) throws {
+        var container = encoder.container(keyedBy: CodingKeys.self)
+        try container.encode(type, forKey: .type)
+        try container.encode(userId, forKey: .userId)
+        if let loop = loop {
+            try container.encode(loop, forKey: .loop)
+        }
+    }
 }
 
 private struct FileKeyPayload: Encodable {