Adopt reusable CI standard (#30)

Squash-merged from claude/adopt-ci-20260616.

QA-approved; all CI checks green on 3b4e3f04.

Agent-Session: deploy-ci-rollout-news-plugin-2026-06-16

phpunit.xml.dist

@@ -1,11 +1,10 @@
 <?xml version="1.0"?>
 <phpunit
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.6/phpunit.xsd"
     bootstrap="tests/bootstrap.php"
     backupGlobals="false"
     colors="true"
-    convertErrorsToExceptions="true"
-    convertNoticesToExceptions="true"
-    convertWarningsToExceptions="true"
 >
     <testsuites>
         <testsuite name="unit">