feat(device): 新增设备在线状态和屏幕状态SSE广播，并修复Redis反序列化问题

- MqttMessageHandler 收到心跳后通过 SseService 广播设备在线状态（含屏幕状态）
- SseService/SseSessionManager 新增设备在线状态和屏幕状态的广播方法
- DeviceOnlineServiceImpl 修复 Redis 反序列化为 LinkedHashMap 时的类型转换问题
- DeviceOnlineServiceImpl 修复批量查询时空 SN 导致索引不对齐的问题

src/main/java/com/youlai/boot/device/service/impl/DeviceOnlineServiceImpl.java

@@ -9,6 +9,7 @@ import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.data.redis.core.RedisTemplate;
 import org.springframework.stereotype.Service;
+import tools.jackson.databind.ObjectMapper;
 
 import java.time.LocalDateTime;
 import java.util.ArrayList;
@@ -33,6 +34,7 @@ public class DeviceOnlineServiceImpl implements DeviceOnlineService {
 
     private final RedisTemplate<String, Object> redisTemplate;
     private final MqttProperties mqttProperties;
+    private final ObjectMapper objectMapper;
 
     @Override
     public void reportHeartbeat(String sn, String ip) {
@@ -101,6 +103,14 @@ public class DeviceOnlineServiceImpl implements DeviceOnlineService {
         if (value instanceof DeviceOnlineVO vo) {
             return vo;
         }
+        // GenericJacksonJsonRedisSerializer 反序列化后可能为 LinkedHashMap，需手动转换
+        if (value != null) {
+            try {
+                return objectMapper.convertValue(value, DeviceOnlineVO.class);
+            } catch (Exception e) {
+                log.warn("转换设备在线状态失败, sn={}", sn, e);
+            }
+        }
         // 离线
         DeviceOnlineVO offline = new DeviceOnlineVO();
         offline.setSerialno(sn);
@@ -115,12 +125,15 @@ public class DeviceOnlineServiceImpl implements DeviceOnlineService {
             return result;
         }
         List<String> keys = new ArrayList<>(sns.size());
+        // 记录有效 SN 的索引映射，避免空 SN 导致 keys 和 sns 索引不对齐
+        List<String> validSns = new ArrayList<>(sns.size());
         for (String sn : sns) {
             if (StrUtil.isBlank(sn)) {
                 continue;
             }
             String key = RedisConstants.Device.ONLINE.replace("{}", sn);
             keys.add(key);
+            validSns.add(sn);
             // 预置离线状态，供缺失 key 时填充
             DeviceOnlineVO offline = new DeviceOnlineVO();
             offline.setSerialno(sn);
@@ -132,10 +145,19 @@ public class DeviceOnlineServiceImpl implements DeviceOnlineService {
             if (values != null) {
                 for (int i = 0; i < values.size(); i++) {
                     Object value = values.get(i);
-                    String sn = sns.get(i);
-                    if (value instanceof DeviceOnlineVO vo) {
-                        result.put(sn, vo);
+                    String sn = validSns.get(i);
+                    if (value == null) {
+                        continue;
                     }
+                    // GenericJacksonJsonRedisSerializer 反序列化 multiGet 结果时
+                    // 返回 LinkedHashMap，需手动转换为 DeviceOnlineVO
+                    DeviceOnlineVO vo;
+                    if (value instanceof DeviceOnlineVO v) {
+                        vo = v;
+                    } else {
+                        vo = objectMapper.convertValue(value, DeviceOnlineVO.class);
+                    }
+                    result.put(sn, vo);
                 }
             }
         } catch (Exception e) {