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/providers/device_info_provider.dart

@@ -0,0 +1,123 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import '../models/device_state.dart';
+import '../services/device_message.dart';
+import '../services/device_message_service.dart';
+import 'serial_provider.dart';
+
+/// 设备信息通知器
+///
+/// 订阅 [DeviceMessageService] 中的 `device_info` 上行消息，
+/// 维护门状态 / 灯状态 / 任务状态，供 UI 直接读取。
+class DeviceInfoNotifier extends StateNotifier<DeviceState> {
+  final DeviceMessageService _msgService;
+  void Function()? _cancelSub;
+
+  DeviceInfoNotifier(this._msgService) : super(const DeviceState()) {
+    _cancelSub = _msgService.subscribe(
+      DeviceMessageType.deviceInfo,
+      _onDeviceInfo,
+    );
+    // 串口断开时无需主动清空 lastInfoAt —— infoStale 会根据
+    // 当前时间与 lastInfoAt 的差值自动判断为「通讯异常」。
+  }
+
+  void _onDeviceInfo(DeviceMessage msg) {
+    final data = msg.data;
+    final light = _parseLight(data['light_status']);
+    final door = _parseDoor(data['door_status']);
+    final task = _parseTask(data['task_status']);
+    state = state.copyWith(
+      lightStatus: light,
+      doorStatus: door,
+      taskStatus: task,
+      lastInfoAt: DateTime.now(),
+    );
+  }
+
+  /// 主动查询设备信息（发送 need_ack=true 的 create_task 之外的 device_info 请求，
+  /// 具体取决于下位机协议约定；目前仅作占位）。
+  Future<void> queryDeviceInfo() async {
+    if (!_msgService.canSend) return;
+    final id = _msgService.nextId();
+    await _msgService.send(DeviceMessage.request(
+      messageId: id,
+      type: DeviceMessageType.deviceInfo,
+      data: const <String, dynamic>{},
+      needAck: true,
+    ));
+  }
+
+  /// 发送灯光控制消息
+  ///
+  /// 主动切换后，下位机通常会通过 device_info 上报新的 light_status
+  /// 覆盖本地状态。
+  Future<bool> toggleLight() async {
+    if (!_msgService.canSend) return false;
+    final next = state.lightStatus == DeviceLightStatus.on ? 'off' : 'on';
+    final id = _msgService.nextId();
+    final ok = await _msgService.send(DeviceMessage.request(
+      messageId: id,
+      type: DeviceMessageType.lightControl,
+      data: {'status': next},
+      needAck: true,
+    ));
+    if (ok) {
+      // 乐观更新；下位机的 device_info 上报会作为最终一致来源
+      state = state.copyWith(
+        lightStatus: next == 'on' ? DeviceLightStatus.on : DeviceLightStatus.off,
+      );
+    }
+    return ok;
+  }
+
+  /// 显式设定灯光
+  Future<bool> setLight(bool on) async {
+    if (!_msgService.canSend) return false;
+    if (on && state.lightStatus == DeviceLightStatus.on) return true;
+    if (!on && state.lightStatus == DeviceLightStatus.off) return true;
+    final id = _msgService.nextId();
+    final ok = await _msgService.send(DeviceMessage.request(
+      messageId: id,
+      type: DeviceMessageType.lightControl,
+      data: {'status': on ? 'on' : 'off'},
+      needAck: true,
+    ));
+    if (ok) {
+      state = state.copyWith(
+        lightStatus: on ? DeviceLightStatus.on : DeviceLightStatus.off,
+      );
+    }
+    return ok;
+  }
+
+  @override
+  void dispose() {
+    _cancelSub?.call();
+    _cancelSub = null;
+    super.dispose();
+  }
+
+  // -- 解析 -------------------------------------------------------------
+
+  static DeviceLightStatus _parseLight(dynamic v) =>
+      v == 'on' ? DeviceLightStatus.on : DeviceLightStatus.off;
+
+  static DeviceDoorStatus _parseDoor(dynamic v) =>
+      v == 'open' ? DeviceDoorStatus.open : DeviceDoorStatus.close;
+
+  static DeviceTaskStatus _parseTask(dynamic v) {
+    return switch (v) {
+      'running' => DeviceTaskStatus.running,
+      'pause' => DeviceTaskStatus.pause,
+      _ => DeviceTaskStatus.idle,
+    };
+  }
+}
+
+/// 设备信息 Provider
+final deviceInfoProvider =
+    StateNotifierProvider<DeviceInfoNotifier, DeviceState>((ref) {
+  final service = ref.watch(deviceMessageServiceProvider);
+  return DeviceInfoNotifier(service);
+});

lib/features/device/providers/serial_provider.dart

@@ -0,0 +1,82 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import '../../../core/database/database_service.dart';
+import '../models/serial_config.dart';
+import '../services/device_message_service.dart';
+import '../services/json_protocol.dart';
+import '../services/runner_interface.dart';
+import '../services/serial_port_service.dart';
+import '../services/serial_runner.dart';
+
+/// 串口服务单例
+final serialPortServiceProvider = Provider<SerialPortService>((ref) {
+  final service = SerialPortService();
+  ref.onDispose(service.dispose);
+  return service;
+});
+
+/// JSON 协议编解码器（可在调试/真机协议不一致时整体替换）
+final jsonProtocolProvider = Provider<JsonProtocolService>((ref) {
+  return JsonProtocolService();
+});
+
+/// 设备消息分发服务
+///
+/// 集中处理 JSON 消息的发送与订阅；下游 Provider 各自订阅感兴趣的类型。
+final deviceMessageServiceProvider =
+    Provider<DeviceMessageService>((ref) {
+  final serial = ref.watch(serialPortServiceProvider);
+  final protocol = ref.watch(jsonProtocolProvider);
+  final service = DeviceMessageService(serial: serial, protocol: protocol);
+  ref.onDispose(service.dispose);
+  return service;
+});
+
+/// 当前串口配置（设置页修改后通过 notifier 写入并持久化）
+class SerialConfigNotifier extends StateNotifier<SerialConfig> {
+  final SettingsConfigRepository _repo;
+
+  SerialConfigNotifier(this._repo) : super(SerialConfig.defaults) {
+    _load();
+  }
+
+  Future<void> _load() async {
+    state = await _repo.read();
+  }
+
+  /// 修改并持久化
+  Future<void> update(SerialConfig Function(SerialConfig) mutator) async {
+    final next = mutator(state);
+    state = next;
+    await _repo.write(next);
+  }
+
+  /// 重置为默认值
+  Future<void> reset() => update((_) => SerialConfig.defaults);
+}
+
+/// 串口配置仓库：把 [SerialConfig] 以 JSON 形式存到 settings 表
+class SettingsConfigRepository {
+  static const _key = 'serial_config';
+  final DatabaseService _db = DatabaseService.instance;
+
+  Future<SerialConfig> read() async {
+    final raw = await _db.readSetting(_key);
+    return SerialConfig.fromJsonString(raw);
+  }
+
+  Future<void> write(SerialConfig config) async {
+    await _db.writeSetting(_key, config.toJsonString());
+  }
+}
+
+final serialConfigProvider =
+    StateNotifierProvider<SerialConfigNotifier, SerialConfig>((ref) {
+  return SerialConfigNotifier(SettingsConfigRepository());
+});
+
+/// 运行器实例（基于 JSON 协议与设备消息服务）
+final runnerProvider = Provider<Runner>((ref) {
+  final msgService = ref.watch(deviceMessageServiceProvider);
+  return JsonSerialRunner(messageService: msgService);
+});