fix(ipam): 修复IP管理页面网段筛选不生效及下拉框过窄

- Ips.vue: el-select 添加 width: 280px，修复网段下拉框过窄
- Ips.vue: query 参数 networkId → network_id（与 FastAPI snake_case 一致）
- Scan.vue: el-select 用 network.id 代替整个 network 对象作为 value，修复切换网段不生效
- enhanced_scan_service.py: 替换失效的 scapy ARP 扫描为 arp-scan 命令；扫描结果自动创建缺失 IP 记录

backend/app/core/config.py

@@ -0,0 +1,35 @@
+from pydantic_settings import BaseSettings
+from typing import Optional
+
+
+class Settings(BaseSettings):
+    # 应用配置
+    APP_NAME: str = "IPAM Management System"
+    APP_VERSION: str = "0.1.0"
+    DEBUG: bool = True
+
+    # 数据库配置
+    DATABASE_URL: str = "mysql+pymysql://ipam:***@localhost:3308/ipam"
+
+    # Redis配置
+    REDIS_URL: str = "redis://localhost:6379/0"
+
+    # Celery配置
+    CELERY_BROKER_URL: str = "redis://localhost:6379/1"
+    CELERY_RESULT_BACKEND: str = "redis://localhost:6379/2"
+
+    # JWT配置
+    SECRET_KEY: str = "your-super-secret-key-here-change-in-production"
+    ALGORITHM: str = "HS256"
+    ACCESS_TOKEN_EXPIRE_MINUTES: int = 60 * 24 * 7
+
+    # 扫描配置
+    PING_TIMEOUT: int = 2
+    PING_RETRIES: int = 2
+    SCAN_CONCURRENCY: int = 50
+
+    class Config:
+        env_file = ".env"
+
+
+settings = Settings()