feat(alerts): 告警中心增加飞书机器人告警推送功能

1. 新增 feishu_service.py: 飞书自定义机器人 webhook 推送
   - 支持卡片消息(interactive)，按告警级别着色
   - 支持签名校验(HMAC-SHA256)
   - 支持最低级别过滤 + 告警类型白名单
2. alert_service.create_alert 创建新告警时自动推飞书
   - 仅新告警推送，去重告警不刷屏
   - 推送失败不影响告警创建
3. alerts.py 新增两个接口:
   - GET /alerts/notify/feishu/status 查看配置状态
   - POST /alerts/notify/feishu/test 发送测试告警
4. config.py + .env.example 增加 FEISHU_* 配置项
   (WEBHOOK_URL / SECRET / ENABLED / MIN_SEVERITY / ALERT_TYPES)

backend/app/api/v1/alerts.py

@@ -181,3 +181,45 @@ def detect_offline_devices(db: Session = Depends(get_db)):
         "count": len(offline_devices),
         "devices": offline_devices
     }
+
+
+# ========== 飞书告警通知 ==========
+
+@router.get("/notify/feishu/status", summary="获取飞书通知配置状态")
+def get_feishu_status():
+    """查看飞书通知是否已配置（不返回密钥等敏感信息）"""
+    from app.services.feishu_service import get_feishu_service
+    svc = get_feishu_service()
+    return {
+        "enabled": svc.enabled,
+        "configured": bool(svc.webhook_url),
+        "webhook_set": bool(svc.webhook_url),
+        "secret_set": bool(svc.secret),
+        "min_severity": svc.min_severity,
+        "alert_types": svc.alert_types,
+        "cani_push": svc.is_configured(),
+    }
+
+
+@router.post("/notify/feishu/test", summary="发送飞书测试告警")
+def test_feishu_notification():
+    """发送一条测试告警到飞书，验证 webhook 配置是否正确"""
+    from app.services.feishu_service import get_feishu_service
+    svc = get_feishu_service()
+    if not svc.is_configured():
+        raise HTTPException(
+            status_code=400,
+            detail="飞书通知未启用或未配置 webhook。请在 backend/.env 设置 FEISHU_ENABLED=true 和 FEISHU_WEBHOOK_URL"
+        )
+    ok = svc.send_alert({
+        "alert_type": "new_device_detected",
+        "severity": "warning",
+        "title": "飞书通知测试",
+        "message": "这是一条测试告警，用于验证飞书机器人 webhook 配置是否正常。",
+        "ip_address_str": "172.16.0.1",
+        "mac_address": "00:11:22:33:44:55",
+    })
+    if ok:
+        return {"message": "飞书测试通知发送成功", "success": True}
+    raise HTTPException(status_code=500, detail="飞书测试通知发送失败，请检查 webhook 地址和日志")
+