build(compose): pin default network subnet to 172.30.0.0/24 for host firewall rules

Co-Authored-By: Claude Fable 5.1 <[email protected]>

docker-compose.yml

@@ -125,3 +125,10 @@ volumes:
   umt-pg-data:
   umt-data:
   umt-camofox:
+
+networks:
+  # 固定网段(属于 172.16.0.0/12),便于宿主防火墙按网段放行容器到宿主的代理/中继端口
+  default:
+    ipam:
+      config:
+        - subnet: ${UMT_SUBNET:-172.30.0.0/24}