refactor(service): 删除MQTT旧代码 + 修复边缘节点重复显示问题

**删除MQTT旧代码：**
- 删除 mqtt_service.py（已废弃的空壳）
- 从 config.py 删除 MQTTConfig 类和相关配置
- 从 schemas.py 删除 mqtt 字段
- 从 alert_service.py 删除 create_alert_from_mqtt 方法
- 告警上报已改为 HTTP + COS 方案，MQTT机制完全废弃

**修复边缘节点重复显示（方案A）：**
- 清理 edge_devices 表历史数据（删除 edge_device_001、edge_inference_device）
- 禁用 DeviceService 的 handle_heartbeat 自动创建设备功能
- 边缘端未实现心跳机制，告警数从 alarm_event 表统计
- 运行时长、处理帧数字段设为 null（无心跳机制，不可用）
- 添加 count_alarms_by_edge_node 方法统计边缘节点告警数

**影响范围：**
- /admin-api/aiot/edge/device/page 接口返回数据调整
- /admin-api/aiot/edge/device/get 接口返回数据调整
- 确保不破坏现有功能（告警上报已改为HTTP）

app/routers/yudao_aiot_edge.py

@@ -7,6 +7,9 @@ API 路径规范：
     - /admin-api/aiot/edge/device/page - 分页查询设备
     - /admin-api/aiot/edge/device/get - 获取设备详情
     - /admin-api/aiot/edge/device/statistics - 设备统计
+
+注意：边缘端未实现心跳机制，因此运行时长/处理帧数等实时指标不可用。
+告警数统计从 alarm_event 表中提取 edge_node_id 字段。
 """
 
 from fastapi import APIRouter, Query, Depends, HTTPException
@@ -14,6 +17,7 @@ from typing import Optional
 
 from app.yudao_compat import YudaoResponse, get_current_user
 from app.services.device_service import get_device_service, DeviceService
+from app.services.alarm_event_service import get_alarm_event_service, AlarmEventService
 
 router = APIRouter(prefix="/admin-api/aiot/edge", tags=["AIoT-边缘设备"])
 
@@ -24,9 +28,10 @@ async def get_device_page(
     pageSize: int = Query(20, ge=1, le=100, description="每页大小"),
     status: Optional[str] = Query(None, description="设备状态: online/offline/error"),
     service: DeviceService = Depends(get_device_service),
+    alarm_service: AlarmEventService = Depends(get_alarm_event_service),
     current_user: dict = Depends(get_current_user)
 ):
-    """分页查询边缘设备列表"""
+    """分页查询边缘设备列表（告警数从 alarm_event 表统计）"""
     devices, total = service.get_devices(
         status=status,
         page=pageNo,
@@ -36,16 +41,21 @@ async def get_device_page(
     device_list = []
     for device in devices:
         device_dict = device.to_dict()
+        device_id = device_dict.get("device_id")
+
+        # 从 alarm_event 表统计告警数
+        alerts_count = alarm_service.count_alarms_by_edge_node(device_id)
+
         device_list.append({
             "id": device_dict.get("id"),
-            "deviceId": device_dict.get("device_id"),
+            "deviceId": device_id,
             "deviceName": device_dict.get("device_name"),
             "status": device_dict.get("status"),
             "statusName": _get_status_name(device_dict.get("status")),
             "lastHeartbeat": device_dict.get("last_heartbeat"),
-            "uptimeSeconds": device_dict.get("uptime_seconds"),
-            "framesProcessed": device_dict.get("frames_processed"),
-            "alertsGenerated": device_dict.get("alerts_generated"),
+            "uptimeSeconds": None,  # 无心跳机制，不可用
+            "framesProcessed": None,  # 无心跳机制，不可用
+            "alertsGenerated": alerts_count,  # 从 alarm_event 表统计
             "ipAddress": device_dict.get("ip_address"),
             "streamCount": device_dict.get("stream_count"),
             "configVersion": device_dict.get("config_version"),
@@ -65,24 +75,30 @@ async def get_device_page(
 async def get_device(
     id: str = Query(..., description="设备ID"),
     service: DeviceService = Depends(get_device_service),
+    alarm_service: AlarmEventService = Depends(get_alarm_event_service),
     current_user: dict = Depends(get_current_user)
 ):
-    """获取设备详情"""
+    """获取设备详情（告警数从 alarm_event 表统计）"""
     device = service.get_device(id)
     if not device:
         raise HTTPException(status_code=404, detail="设备不存在")
 
     device_dict = device.to_dict()
+    device_id = device_dict.get("device_id")
+
+    # 从 alarm_event 表统计告警数
+    alerts_count = alarm_service.count_alarms_by_edge_node(device_id)
+
     return YudaoResponse.success({
         "id": device_dict.get("id"),
-        "deviceId": device_dict.get("device_id"),
+        "deviceId": device_id,
         "deviceName": device_dict.get("device_name"),
         "status": device_dict.get("status"),
         "statusName": _get_status_name(device_dict.get("status")),
         "lastHeartbeat": device_dict.get("last_heartbeat"),
-        "uptimeSeconds": device_dict.get("uptime_seconds"),
-        "framesProcessed": device_dict.get("frames_processed"),
-        "alertsGenerated": device_dict.get("alerts_generated"),
+        "uptimeSeconds": None,  # 无心跳机制，不可用
+        "framesProcessed": None,  # 无心跳机制，不可用
+        "alertsGenerated": alerts_count,  # 从 alarm_event 表统计
         "ipAddress": device_dict.get("ip_address"),
         "streamCount": device_dict.get("stream_count"),
         "configVersion": device_dict.get("config_version"),