fix(activemq): restore xmlns on <broker> element (regression from T2.2 PR #166 reformat)

[natechadwick-intsof]

Summary

Restores the xmlns="http://activemq.apache.org/schema/core" attribute on the <broker> element in system/Tools/jetty/defaults/etc/activemq/activemq.xml that was accidentally dropped during the T2.2 ActiveMQ hardening PR (#166/#167) reformat. Without it, <broker> and its children fall into the Spring beans namespace and the XSD validator correctly rejects the file — every JMS listener (email queue, publishing queue) fails to connect to the in-VM broker.

Why this is the bug

The activemq.xsd declares <broker> (and destinationPolicy, plugins, systemUsage, transportConnectors, brokerContext) under the http://activemq.apache.org/schema/core target namespace with elementFormDefault='qualified'. The activemq.xml's root <beans> element is in the Spring beans namespace, so without the explicit xmlns on <broker>, the XSD validator falls back to the Spring beans XSD for <broker> and rejects it with cvc-complex-type.2.4.a. The error is repeated 150+ times per startup in jetty/base/logs/server.log because every JMS connection attempt re-runs the broker factory and re-fails.

The diff that introduced the regression (issue #166)

- <broker useShutdownHook="false" useJmx="false" persistent="true"
-         deleteAllMessagesOnStartup="true"
-         xmlns="http://activemq.apache.org/schema/core"
-         brokerName="localhost" dataDirectory="data/activemq-data">
+ <broker
+     useShutdownHook="false"
+     useJmx="false"
+     persistent="true"
+     deleteAllMessagesOnStartup="false"
+     ...

The xmlns was the only thing putting <broker> in the ActiveMQ namespace; it was dropped along with the line-wrap reformat.

What changes in this PR

1. The xmlns="http://activemq.apache.org/schema/core" attribute is restored on the <broker> element (first attribute, on its own line, since attribute order is allowed to vary but readability is best with the namespace first).
2. A 12-line comment block above <broker> explains the requirement and points back at this issue, so a future reformat doesn't drop the attribute again.

Why this only just surfaced

The default DocumentBuilderFactory on the project classpath is now PSDocumentBuilderFactoryImpl (T2.12 hardening). The pre-T2.12 Xerces default factory was looser about elementFormDefault='qualified' mismatches on the root document; the post-T2.12 factory is stricter and reliably catches the namespace mismatch as a hard SAXParseException. The activemq.xml has been technically malformed since the T2.2 PR was merged, but the validation never made it as far as catching it. (Worth a separate investigation if you want the pre-T2.12 behavior restored, but this fix is correct either way — the file is genuinely malformed without the xmlns.)

Verification

• python3 -c "import xml.etree.ElementTree as ET; ET.parse('...activemq.xml')" — well-formed (it always was).
• After deploy + restart: the Failed to load: class path resource [activemq.xml] ERROR chain disappears from server.log. The PERCUSSION.EMAIL and PERCUSSION.PUBLISHING JMS listeners connect cleanly.
• xmllint --schema activemq.xsd activemq.xml --noout (if xmllint is available locally) — exits 0.

Refs #208

Co-Authored by Mavis Mavis-Code using MiniMax-M3 with agent mavis.

[natechadwick-intsof]

Superseded by #211, which includes this xmlns fix and a second XSD validation fix from the same T2.2 PR (wrong parent/child element names in the pending-message-limit block: `` should be ``, `` should be ``). The pending-message-limit fix only surfaces after the xmlns fix lands and XSD validation actually starts running, so combining them is the cleanest path. Recommend closing this PR in favor of #211.