feat: add PlayMode enum (single=0, loop=1)

Sources/DuooomiBleSDK/Models/PlayMode.swift

@@ -0,0 +1,10 @@
+import Foundation
+
+/// 播放模式（设备端协议字段 `loop`）。
+///
+/// - `single` (0): 单播 —— 设备播完一次后停止
+/// - `loop`   (1): 循环播放 —— 设备循环播放当前内容
+public enum PlayMode: Int, Codable, Equatable {
+    case single = 0
+    case loop = 1
+}

Tests/DuooomiBleSDKTests/PlayModeTests.swift

@@ -0,0 +1,22 @@
+import XCTest
+@testable import DuooomiBleSDK
+
+final class PlayModeTests: XCTestCase {
+    func testRawValues() {
+        XCTAssertEqual(PlayMode.single.rawValue, 0)
+        XCTAssertEqual(PlayMode.loop.rawValue, 1)
+    }
+
+    func testInitFromRawValue() {
+        XCTAssertEqual(PlayMode(rawValue: 0), .single)
+        XCTAssertEqual(PlayMode(rawValue: 1), .loop)
+        XCTAssertNil(PlayMode(rawValue: 2))
+    }
+
+    func testCodableRoundTrip() throws {
+        let data = try JSONEncoder().encode(PlayMode.loop)
+        XCTAssertEqual(String(data: data, encoding: .utf8), "1")
+        let decoded = try JSONDecoder().decode(PlayMode.self, from: Data("0".utf8))
+        XCTAssertEqual(decoded, .single)
+    }
+}