feat: 高德IoT v5 API升级、电子围栏管理、设备绑定自动考勤

- 前向地理编码升级为高德IoT v5 API (POST restapi.amap.com/v5/position/IoT)
- 修复LBS定位偏差: 添加network=LTE参数区分4G/2G, bts格式补充cage字段
- 新增电子围栏管理模块 (circle/polygon/rectangle), 支持地图绘制和POI搜索
- 新增设备-围栏多对多绑定 (DeviceFenceBinding/DeviceFenceState)
- 围栏自动考勤引擎 (fence_checker.py): haversine距离、ray-casting多边形判定、容差机制、防抖
- TCP位置上报自动检测围栏进出, 生成考勤记录并WebSocket广播
- 前端围栏页面: 绑定设备弹窗、POI搜索定位、左侧围栏面板
- 新增fence_attendance WebSocket topic

via [HAPI](https://hapi.run)

Co-Authored-By: HAPI <noreply@hapi.run>

app/routers/commands.py

@@ -5,7 +5,7 @@ API endpoints for sending commands / messages to devices and viewing command his
 
 import logging
 import math
-from datetime import datetime, timezone
+from app.config import now_cst
 
 from fastapi import APIRouter, Depends, HTTPException, Query, Request
 from pydantic import BaseModel, Field
@@ -129,7 +129,7 @@ async def _send_to_device(
         )
 
     command_log.status = "sent"
-    command_log.sent_at = datetime.now(timezone.utc)
+    command_log.sent_at = now_cst()
     await db.flush()
     await db.refresh(command_log)
 
@@ -290,7 +290,7 @@ async def batch_send_command(request: Request, body: BatchCommandRequest, db: As
                 device.imei, body.command_type, body.command_content
             )
             cmd_log.status = "sent"
-            cmd_log.sent_at = datetime.now(timezone.utc)
+            cmd_log.sent_at = now_cst()
             await db.flush()
             await db.refresh(cmd_log)
             results.append(BatchCommandResult(