build: add container Maven settings without mirror

Add settings-container.xml for Docker builds that connects directly to
Maven Central, avoiding stale mirrors during CI builds.

.mvn/settings-container.xml

@@ -0,0 +1,36 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<!--
+  ~ Copyright 2016-present the IoT DC3 original author or authors.
+  ~
+  ~ This program is free software: you can redistribute it and/or modify
+  ~ it under the terms of the GNU Affero General Public License as
+  ~ published by the Free Software Foundation, either version 3 of the
+  ~ License, or (at your option) any later version.
+  ~
+  ~ This program is distributed in the hope that it will be useful,
+  ~ but WITHOUT ANY WARRANTY; without even the implied warranty of
+  ~ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  ~ GNU Affero General Public License for more details.
+  ~
+  ~ You should have received a copy of the GNU Affero General Public License
+  ~ along with this program.  If not, see <https://www.gnu.org/licenses/>.
+  -->
+
+<!--
+  Maven settings used INSIDE the Dockerfile builder stage.
+
+  Difference from .mvn/settings.xml: no <mirrors>. Pulling directly from
+  Maven Central avoids the situation where a freshly-released artifact
+  (e.g. a new dc3-parent version) is available on Maven Central but has
+  not yet propagated to the Aliyun mirror — which would otherwise break
+  container builds for hours after a release.
+
+  Local developers continue to use .mvn/settings.xml (with Aliyun mirror)
+  for faster everyday builds.
+-->
+<settings xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+          xmlns="http://maven.apache.org/SETTINGS/1.0.0"
+          xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">
+
+</settings>