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/services/alert_service.py

@@ -12,6 +12,18 @@ from app.models.alert import (
 from app.models.network import Network, IPAddress
 from app.models.snmp import NetworkDevice, ARPEntry
 
+# 飞书告警通知（延迟导入避免循环依赖）
+_feishu_service = None
+
+
+def _get_feishu_service():
+    global _feishu_service
+    if _feishu_service is None:
+        from app.services.feishu_service import get_feishu_service
+        _feishu_service = get_feishu_service()
+    return _feishu_service
+
+
 logger = logging.getLogger(__name__)
 
 
@@ -70,6 +82,22 @@ class AlertService:
         db.refresh(alert)
 
         logger.info(f"创建告警: {alert_type} - {title}")
+
+        # 飞书告警通知（仅新创建的告警推送；existing 去重返回的不会走到这里，避免刷屏）
+        try:
+            _get_feishu_service().send_alert({
+                "alert_type": alert_type.value if hasattr(alert_type, "value") else str(alert_type),
+                "severity": severity.value if hasattr(severity, "value") else str(severity),
+                "title": title,
+                "message": message,
+                "ip_address_str": ip_address_str,
+                "mac_address": mac_address,
+                "conflicting_mac": conflicting_mac,
+                "usage_percent": usage_percent,
+            })
+        except Exception as e:
+            logger.error(f"飞书告警通知失败（不影响告警创建）: {e}")
+
         return alert
 
     @staticmethod