feat(device): 实现下位机 JSON 协议（data model 对齐）

按 docs/下位机交互数据模型.md 重构串口协议层：

协议层
- 新增 DeviceMessage 模型，对应 message_id/type/ack/need_ack/data
- 新增 JsonProtocolService，4 字节大端长度前缀 + UTF-8 JSON 帧
- 删除原二进制协议（serial_protocol.dart）

服务层
- 新增 DeviceMessageService，集中收发并按 type 分发
- 重写 SerialRunner 为 JsonSerialRunner，使用 create_task/control 消息

数据模型
- DeviceState 增加 doorStatus/lightStatus/taskStatus/lastInfoAt
- 新增 DeviceInfoNotifier 订阅 device_info 上行
- 灯光按钮接通 light_control 消息

测试
- 新增 device_protocol_test.dart（14 用例）
- 修复 models_test.dart 残留的 Step mixSpeed/blowSpeed 错误

lib/features/device/models/device_state.dart

@@ -1,18 +1,64 @@
-/// 设备状态模型
-enum DeviceStatus { idle, running, paused, error }
+/// 设备运行状态
+///
+/// 与下位机 `device_info.task_status` 字段对齐：
+/// - `running` 运行中
+/// - `pause`   暂停
+/// - `idle`    空闲
+enum DeviceTaskStatus { running, pause, idle }
 
-/// 设备状态数据
+/// 设备门状态
+///
+/// 与下位机 `device_info.door_status` 字段对齐：
+/// - `open`  开
+/// - `close` 关
+enum DeviceDoorStatus { open, close }
+
+/// 设备灯光状态
+///
+/// 与下位机 `device_info.light_status` / `light_control.status` 字段对齐：
+/// - `on`  开
+/// - `off` 关
+enum DeviceLightStatus { on, off }
+
+/// 上位机内部统一的设备状态模型
+///
+/// 既承载 [DeviceState]（运行态监控），也承载下位机 `device_info` 上报
+/// 的门状态 / 灯光状态 / 任务状态，供 UI 各处订阅展示与联动。
 class DeviceState {
+  /// 本机内部识别的运行状态（用于驱动运行/暂停/完成流程）
   final DeviceStatus status;
-  final String? currentProgram;
-  final String? currentPosition;
-  final int? currentStepNo;
-  final String? currentStepName;
-  final int? remainingSeconds;
-  final double? progress;
-  final bool lightingOn;
 
-  DeviceState({
+  /// 当前运行程序名（仅运行态有效）
+  final String? currentProgram;
+
+  /// 当前步骤的孔位（例如 A1）
+  final String? currentPosition;
+
+  /// 当前步骤号
+  final int? currentStepNo;
+
+  /// 当前步骤名
+  final String? currentStepName;
+
+  /// 当前步骤剩余时间（秒）
+  final int? remainingSeconds;
+
+  /// 总进度 [0, 1]
+  final double? progress;
+
+  /// 灯光状态（来自 device_info，主动权在下位机）
+  final DeviceLightStatus lightStatus;
+
+  /// 门状态（来自 device_info）
+  final DeviceDoorStatus doorStatus;
+
+  /// 任务状态（来自 device_info）
+  final DeviceTaskStatus taskStatus;
+
+  /// 上次 device_info 上报的时间，便于 UI 显示「通讯正常 / 已断开」
+  final DateTime? lastInfoAt;
+
+  const DeviceState({
     this.status = DeviceStatus.idle,
     this.currentProgram,
     this.currentPosition,
@@ -20,7 +66,10 @@ class DeviceState {
     this.currentStepName,
     this.remainingSeconds,
     this.progress,
-    this.lightingOn = false,
+    this.lightStatus = DeviceLightStatus.off,
+    this.doorStatus = DeviceDoorStatus.close,
+    this.taskStatus = DeviceTaskStatus.idle,
+    this.lastInfoAt,
   });
 
   bool get isRunning => status == DeviceStatus.running;
@@ -28,6 +77,18 @@ class DeviceState {
   bool get isIdle => status == DeviceStatus.idle;
   bool get hasError => status == DeviceStatus.error;
 
+  bool get lightingOn => lightStatus == DeviceLightStatus.on;
+  bool get doorOpen => doorStatus == DeviceDoorStatus.open;
+
+  /// 下位机超过该时间未上报则视为通讯异常
+  static const Duration infoStaleAfter = Duration(seconds: 10);
+
+  bool get infoStale {
+    final ts = lastInfoAt;
+    if (ts == null) return true;
+    return DateTime.now().difference(ts) > infoStaleAfter;
+  }
+
   String statusText() {
     switch (status) {
       case DeviceStatus.running:
@@ -46,7 +107,9 @@ class DeviceState {
     final hours = remainingSeconds! ~/ 3600;
     final minutes = (remainingSeconds! % 3600) ~/ 60;
     final seconds = remainingSeconds! % 60;
-    return '${hours.toString().padLeft(2, '0')}:${minutes.toString().padLeft(2, '0')}:${seconds.toString().padLeft(2, '0')}';
+    return '${hours.toString().padLeft(2, '0')}:'
+        '${minutes.toString().padLeft(2, '0')}:'
+        '${seconds.toString().padLeft(2, '0')}';
   }
 
   DeviceState copyWith({
@@ -57,17 +120,28 @@ class DeviceState {
     String? currentStepName,
     int? remainingSeconds,
     double? progress,
-    bool? lightingOn,
+    DeviceLightStatus? lightStatus,
+    DeviceDoorStatus? doorStatus,
+    DeviceTaskStatus? taskStatus,
+    DateTime? lastInfoAt,
+    bool clearProgram = false,
+    bool clearProgress = false,
   }) {
     return DeviceState(
       status: status ?? this.status,
-      currentProgram: currentProgram ?? this.currentProgram,
+      currentProgram: clearProgram ? null : (currentProgram ?? this.currentProgram),
       currentPosition: currentPosition ?? this.currentPosition,
       currentStepNo: currentStepNo ?? this.currentStepNo,
       currentStepName: currentStepName ?? this.currentStepName,
       remainingSeconds: remainingSeconds ?? this.remainingSeconds,
-      progress: progress ?? this.progress,
-      lightingOn: lightingOn ?? this.lightingOn,
+      progress: clearProgress ? null : (progress ?? this.progress),
+      lightStatus: lightStatus ?? this.lightStatus,
+      doorStatus: doorStatus ?? this.doorStatus,
+      taskStatus: taskStatus ?? this.taskStatus,
+      lastInfoAt: lastInfoAt ?? this.lastInfoAt,
     );
   }
-}
+}
+
+/// 简单的状态枚举（与 [DeviceState.status] 配合使用）
+enum DeviceStatus { idle, running, paused, error }